How RNA-DNA Hybrids Affect Genome Stability: RNase H1, RNase H2, and R-loop Regulatory Mechanisms

RNA-DNA hybrids are nucleic acid structures formed by pairing between an RNA strand and a DNA template strand. Typical forms include transcription-associated R-loops and hybrid regions formed after ribonucleotides are incorporated into DNA. RNase H1, RNase H2, helicases, topoisomerases, and RNA-processing factors collectively determine whether these structures participate in normal regulation or become sources of replication stress, DNA damage, and genome instability.

Keywords: RNA-DNA hybrid; R-loop; RNase H1; RNase H2; genome stability; transcription-replication conflict; replication stress; ribonucleotide excision repair; DNA damage; DRIP-qPCR

1 Structural Features of RNA-DNA Hybrids and R-loops

1.1 Basic structure

An RNA-DNA hybrid is formed by base pairing between an RNA strand and a complementary DNA strand. When this structure occurs within double-stranded DNA and the other DNA strand is displaced to form a single-stranded DNA region, it constitutes a typical R-loop. R-loops are not simply abnormal structures. They can participate in normal transcriptional regulation at promoters, termination regions, immunoglobulin genes, mitochondrial DNA replication regions, and certain regulatory regions. However, when their location, duration, or clearance efficiency becomes imbalanced, the risk of DNA damage increases.

(1) Transcription-associated R-loops

During transcription, nascent RNA can rehybridize with the template DNA strand. R-loops are more likely to form in regions with high GC content, G-rich RNA, strong transcriptional activity, impaired RNA processing, or elevated DNA topological stress. This structure exposes the non-template DNA strand as single-stranded DNA, making it more susceptible to nucleases, deaminases, or replication fork collisions.

(2) Replication-associated RNA-DNA hybrids

During replication, RNA primers, residual Okazaki fragment processing intermediates, and ribonucleotides incorrectly incorporated into DNA can all generate RNA-DNA hybrid features. Unlike classical transcription-associated R-loops, these structures are more directly linked to DNA replication maturation, ribonucleotide excision repair, and replication fork stability.

(3) Mitochondrial RNA-DNA hybrids

Mitochondrial DNA replication and transcription are highly coupled, and RNA-DNA hybrids can participate in replication initiation and post-transcriptional processing. RNase H1 is particularly important in mitochondria. Its loss or functional insufficiency can affect mitochondrial DNA replication, copy number maintenance, and respiratory chain function.

1.2 Dual roles of R-loops

R-loops have both regulatory and damaging properties. Stable, transient, and precisely localized R-loops can participate in transcription termination, promoter opening, chromatin regulation, and immune-related gene rearrangement. Persistent accumulation or mislocalization of R-loops can impede replication fork progression, induce transcription-replication conflicts, promote double-strand breaks, and activate the DNA damage response. In experimental interpretation, R-loops should not be simply equated with “harmful structures”; their formation sites, cell-cycle stage, transcriptional status, and DNA damage readouts should be analyzed together.

Table 1 Major Sources of RNA-DNA Hybrids and Interpretation Focus

Structural Source	Typical Region	Related Mechanism	Risk Point	Recommended Combined Indicators
Transcription-associated R-loops	Promoters, termination regions, highly transcribed genes, GC-rich regions	Nascent RNA rehybridizes with the template strand	Transcription-replication conflict, single-stranded DNA exposure	DRIP-qPCR, γH2AX, RNA Pol II, replication fork indicators
Residual RNA primers	Replication origins, Okazaki fragment maturation regions	Incomplete RNA primer removal	Abnormal replication maturation	RNase H2, FEN1, LIG1, replication stress indicators
Ribonucleotide incorporation into DNA	Genome-wide replication products	rNMP misincorporation by DNA polymerase	DNA breaks, mutations, replication blockage	RNase H2, RER-related indicators, alkali-sensitive break analysis
Mitochondrial RNA-DNA hybrids	mtDNA replication and transcription regions	Replication initiation, RNA processing	Reduced mtDNA copy number, respiratory chain dysfunction	RNase H1, mtDNA copy number, OXPHOS indicators
Telomere-associated R-loops	Telomeres and TERRA transcription regions	TERRA-DNA hybrid formation	Telomere replication stress and telomere instability	TERRA, telomere FISH, DNA damage foci

2 Functional Division between RNase H1 and RNase H2

2.1 RNase H1

RNase H1 mainly cleaves the RNA strand in relatively long RNA-DNA hybrids and is efficient in processing continuous RNA-DNA hybrid structures. However, it usually cannot efficiently recognize single ribonucleotides embedded in DNA. Its functions include nuclear genome R-loop clearance and mitochondrial RNA-DNA hybrid processing, and it is especially critical for mitochondrial DNA replication.

(1) Nuclear R-loop processing

RNase H1 overexpression is commonly used to verify whether S9.6 antibody or DRIP signals originate from RNA-DNA hybrids. If DRIP-qPCR signals decrease after RNase H1 treatment, it indicates that RNase H-sensitive hybrid structures exist in that region. If the signal remains unchanged, nonspecific binding, dsRNA signals, or detection background should be considered.

(2) Mitochondrial DNA maintenance

RNase H1 participates in processing mitochondrial RNA primers or RNA-DNA hybrids. RNase H1 insufficiency can lead to abnormal mitochondrial DNA replication, reduced mtDNA copy number, and impaired oxidative phosphorylation. Therefore, mitochondrial models should not be evaluated only by nuclear R-loop detection.

(3) Experimental application boundaries

RNase H1 overexpression can reduce certain R-loops, but excessive expression may alter normal regulatory R-loops and transcriptional status. Functional validation should combine catalytically inactive mutants, localization mutants, DRIP signals, DNA damage, and cell viability.

2.2 RNase H2

RNase H2 is a heterotrimeric complex composed of RNASEH2A, RNASEH2B, and RNASEH2C. It can process RNA-DNA hybrids and recognize single ribonucleotides embedded in DNA duplexes to initiate ribonucleotide excision repair. Compared with RNase H1, RNase H2 is indispensable for removing rNMPs embedded in DNA.

(1) Ribonucleotide excision repair

During replication, DNA polymerases can mistakenly incorporate ribonucleotides. RNase H2 recognizes these sites and cleaves at the RNA-DNA junction, after which DNA polymerases, nucleases, and ligases complete repair. When this process is impaired, rNMPs accumulate in the genome and may induce replication blockage, DNA breaks, and mutations.

(2) R-loop regulation

RNase H2 can also participate in processing some R-loops, but its function should not be simply equated with that of RNase H1. If RNASEH2A/B/C deficiency causes increased R-loop signals, it is necessary to further distinguish whether the increase results from transcription-associated R-loops, rNMP repair defects, or secondary changes caused by replication stress.

(3) Disease relevance

Defects in the RNase H2 complex are closely associated with abnormal nucleic acid metabolism, DNA damage responses, and innate immune activation. If cytosolic DNA, the cGAS-STING pathway, or interferon-stimulated genes are upregulated, genome rNMP accumulation, DNA damage, and R-loop status should be evaluated simultaneously.

Table 2 Functional Differences between RNase H1 and RNase H2

Item	RNase H1	RNase H2
Composition	Single enzyme protein	RNASEH2A/B/C three-subunit complex
Main substrates	Relatively long RNA-DNA hybrids	RNA-DNA hybrids and single rNMPs embedded in DNA
Key functions	R-loop clearance, mitochondrial RNA-DNA hybrid processing	Ribonucleotide excision repair, processing of replication-associated RNA-DNA structures
Mitochondrial relevance	Strong	Usually not regarded as a core enzyme for mitochondrial DNA replication processing
Experimental use	R-loop signal validation, overexpression-mediated clearance experiments	rNMP repair defects, replication stress, and immune activation research
Interpretation risk	Overexpression may affect normal R-loop regulation	Increased R-loops may be an indirect consequence of rNMP accumulation and replication stress

3 Regulatory Network of R-loop Formation and Clearance

3.1 Transcription intensity and RNA processing

Highly transcribed regions are more prone to R-loop formation, but strong transcription does not necessarily lead to R-loop accumulation. RNA capping, splicing, 3'-end processing, and RNA export can reduce the likelihood of nascent RNA rehybridizing with template DNA. When splicing factors, RNA export factors, or transcription termination processes are impaired, nascent RNA remains near chromatin for longer, increasing the probability of R-loop formation. If increased R-loops are observed experimentally, RNA processing or transcription termination abnormalities should also be examined, rather than attributing the phenotype only to RNase H insufficiency.

3.2 DNA topology and chromatin state

Transcription progression generates local supercoiling stress, and negative supercoiling can promote DNA strand separation and increase the opportunity for RNA rehybridization. Topoisomerases, chromatin remodeling factors, and histone modification states can influence the threshold for R-loop formation. TOP1 or TOP2 dysfunction, excessive chromatin openness, or exposure of GC-rich regions can all stabilize R-loops.

3.3 Helicases and nucleic acid-processing factors

Helicases or nucleic acid-processing factors such as SETX, DDX, DHX, PIF1, and FANCM can participate in R-loop resolution, transcription termination, replication fork protection, and DNA repair. Different factors act at different locations: some are more involved in transcription termination regions, some act at replication fork conflict sites, and others are linked to homologous recombination or the Fanconi anemia pathway. When interpreting R-loop phenotypes, the localization and functional context of the specific factor should be considered.

3.4 Replication forks and transcription-replication conflicts

When a replication fork encounters transcription machinery on the same DNA template, R-loops can exacerbate the conflict. Head-on conflicts are usually more likely to cause replication fork stalling and DNA breaks. Co-directional conflicts may also generate replication stress due to RNA-DNA hybrids, RNA Pol II stalling, or abnormal topological stress. R-loop-related genome instability often manifests as reduced replication fork speed, increased fork stalling, elevated γH2AX, and accumulation of 53BP1/RPA foci.

Table 3 R-loop Regulatory Factors and Functional Layers

Regulatory Layer	Representative Factors	Main Role	Common Outcome after Abnormality
RNA processing	Splicing factors, RNA export factors, 3'-end processing factors	Reduce the opportunity for nascent RNA to rehybridize with DNA	Increased transcription-associated R-loops
DNA topology	TOP1, TOP2	Relieve transcription-induced supercoiling stress	Increased DNA strand separation and stabilized R-loops
Helicases	SETX, DDX/DHX family, PIF1, FANCM	Resolve R-loops or protect replication forks	Abnormal transcription termination and increased replication stress
Repair pathways	BRCA1/2, FANCD2, ATR, ATM	Process R-loop-associated damage and replication stress	DSBs and chromosomal instability
Nucleases	RNase H1, RNase H2	Cleave the RNA strand in RNA-DNA hybrids	Accumulation of R-loop- or rNMP-related damage
Chromatin environment	Histone modifications, chromatin remodeling factors	Regulate DNA accessibility and transcriptional status	Altered R-loop formation sites

4 Abnormal RNA-DNA Hybrids and Genome Instability

4.1 Replication stress

R-loops can act as physical barriers ahead of replication forks and can also increase fork stalling by altering DNA topology and chromatin state. Replication stress is usually reflected by reduced replication fork speed, shortened replication tracks in DNA fiber assays, increased RPA single-stranded DNA foci, and ATR pathway activation. If RNase H1 overexpression partially restores replication fork progression, R-loops may be involved in the replication defect.

4.2 DNA double-strand breaks

Single-stranded DNA exposed by R-loops is more prone to damage, and replication fork collision with stable R-loops can also produce breaks. Elevated γH2AX, 53BP1, pATM, and pDNA-PKcs can indicate DNA damage, but these markers alone cannot prove that the damage is caused by R-loops. A more reliable design is to analyze RNase H treatment, R-loop detection, and DNA damage rescue in the same model.

4.3 Mutations and chromosomal rearrangements

Persistent R-loops can increase single-stranded DNA deamination, replication errors, and abnormal involvement of repair pathways. Particular attention should be paid to the relationship between R-loops and mutation patterns near immunoglobulin gene rearrangement regions, germ cell meiosis regions, repetitive sequences, and highly transcribed genes. If BRCA or FANCD2 pathway defects are also present, R-loop-associated damage is more likely to develop into chromosomal instability.

4.4 Innate immune activation

RNase H2 deficiency, impaired rNMP clearance, and R-loop-associated DNA damage can generate abnormal nucleic acid fragments, thereby activating the cGAS-STING pathway or interferon-related pathways. In such models, upregulation of IFNB1, ISG15, CXCL10, and related genes should not be interpreted only as infection-like responses. Nucleic acid metabolic defects, DNA damage, and cytosolic DNA accumulation should also be evaluated.

5 R-loop Detection Methods and Experimental Design

5.1 DRIP-qPCR and DRIP-seq

DRIP methods usually use the S9.6 antibody to recognize RNA-DNA hybrids, followed by qPCR or sequencing to localize R-loop regions. Their advantages are relatively mature workflows and suitability for regional validation and genome-wide screening. The main risk is that S9.6 may also recognize double-stranded RNA or nonspecific nucleic acid structures; therefore, RNase H pretreatment is a critical control.

(1) Regional validation

DRIP-qPCR is suitable for validating R-loop changes at specific gene promoters, termination regions, repetitive sequences, or damage-prone hotspots. Positive regions, negative regions, and RNase H treatment controls should be included to avoid drawing genome-wide conclusions from a single regional signal.

(2) Genome-wide mapping

DRIP-seq can analyze the genome-wide distribution of R-loops, but sample processing, fragmentation methods, antibody batches, and bioinformatics parameters can significantly affect results. Key findings should be confirmed by DRIP-qPCR, RNase H sensitivity validation, and functional experiments.

5.2 S9.6 immunofluorescence

S9.6 immunofluorescence can be used to observe overall intracellular changes in RNA-DNA hybrids and is suitable for initial screening and comparison among cell populations. This method has limited spatial resolution and is easily affected by nucleic acid extraction, fixation methods, and antibody specificity. If the signal is enhanced, it should be further validated by RNase H treatment, nuclease controls, and region-specific detection.

5.3 R-ChIP and enzymatic labeling methods

R-ChIP-like methods use catalytically inactive RNase H variants to bind RNA-DNA hybrids, thereby improving localization specificity. Their advantage is that they can reduce some antibody-related background, but they may also be affected by expression levels, fusion protein localization, and binding preferences. They are suitable for complementing DRIP-seq but should not be used as the only evidence.

5.4 Combined analysis with DNA damage and replication stress

R-loop detection should be combined with functional readouts. Common combinations include DRIP-qPCR plus γH2AX, S9.6 immunofluorescence plus RNase H1 overexpression, DNA fiber assays plus RNase H rescue, and R-loop regional sequencing plus transcriptional analysis. If only R-loop signals increase without changes in replication stress or damage indicators, the pathological significance should be interpreted cautiously.

Table 4 R-loop Detection Methods and Applicable Scenarios

Method	Main Use	Advantage	Key Controls	Main Limitation
DRIP-qPCR	Validation of R-loops at specific sites	Direct quantification, suitable for mechanistic validation	RNase H treatment, negative regions, input DNA	Site selection affects conclusions
DRIP-seq	Genome-wide R-loop profiling	Can identify high-risk regions	RNase H treatment, biological replicates	Strongly affected by antibody background and analysis parameters
S9.6 immunofluorescence	Initial screening of overall intracellular R-loop levels	Can observe differences among cell populations	RNase H treatment, nuclease controls	Limited localization and quantitative precision
R-ChIP	R-loop localization	Higher specificity, suitable for complementary validation	Catalytically inactive control, expression-level control	Depends on fusion protein expression and localization
DNA fiber co-analysis	Evaluate replication fork blockage	Directly assesses replication stress	RNase H1 rescue, replication inhibition control	Technically demanding
γH2AX/53BP1 co-analysis	Evaluate damage consequences	Links R-loops with DNA damage	RNase H rescue, cell-cycle control	Cannot independently prove damage origin

6 Result Interpretation and Common Pitfalls

6.1 Increased R-loops do not necessarily indicate RNase H deficiency

R-loop increases can result from enhanced transcription, RNA-processing defects, elevated topological stress, helicase deficiency, replication fork stalling, or altered chromatin state. Directly attributing increased R-loops to RNase H insufficiency can overlook upstream transcriptional and chromatin factors. RNase H1/H2 expression or activity, RNA-processing factors, transcription levels, and replication stress should be assessed together.

6.2 RNase H1 rescue does not mean all damage originates from R-loops

RNase H1 overexpression can reduce some RNA-DNA hybrids and alleviate replication stress, but it may also alter normal regulatory R-loops. If DNA damage decreases, it should be further confirmed whether the rescue depends on RNase H1 catalytic activity, while excluding indirect effects caused by transcriptional suppression, cell-cycle changes, or reduced cytotoxicity.

6.3 RNase H2 deficiency requires distinguishing rNMP accumulation from R-loop accumulation

One core problem in RNase H2 deficiency is abnormal ribonucleotide excision repair in DNA. R-loop signals, DNA breaks, and immune activation may appear together, but they are not necessarily all caused directly by classical transcription-associated R-loops. rNMP-related detection, alkali-sensitive break analysis, replication stress indicators, and RNase H2 complex subunit expression should be combined for interpretation.

6.4 S9.6 signals must be validated for RNase H sensitivity

Enhanced S9.6 signals do not automatically equal increased R-loops. If RNase H treatment markedly reduces the signal, an RNA-DNA hybrid origin is supported. If the signal does not decrease, dsRNA, nonspecific background, or sample processing problems should be considered. For high-impact conclusions, at least one non-S9.6-dependent method is recommended for cross-validation.

Table 5 Common Abnormal Patterns and Interpretation Paths in R-loop Research

Result Pattern	Possible Explanation	Suggested Additional Experiments
S9.6 signal increases and decreases after RNase H treatment	Increased RNA-DNA hybrids	DRIP-qPCR localization, RNase H1 rescue, transcription-level detection
R-loops increase and γH2AX increases	R-loop-associated damage or replication stress	DNA fiber assay, 53BP1/RPA foci, cell-cycle analysis
RNASEH2 deficiency and ISG upregulation	rNMP accumulation, DNA damage, or cytosolic nucleic acid activation	cGAS-STING markers, rNMP repair analysis, DNA damage detection
RNase H1 overexpression rescues replication fork speed	R-loops participate in replication stress	Catalytically inactive RNase H1 control, DRIP-qPCR validation
R-loops increase but DNA damage does not change	Regulatory R-loops or damage threshold not reached	Analyze site distribution, transcriptional regulation, and long-term stability
Antibody detection and sequencing results are inconsistent	Antibody background, sample processing differences, or region selection differences	Add RNase H controls and independent method validation

7 Experimental Design Recommendations

7.1 Mechanistic studies

If the goal is to prove that a protein regulates R-loops, four levels should be completed: R-loop changes, RNase H sensitivity, functional consequences, and rescue validation. Showing only S9.6 signal changes is insufficient to support a mechanistic conclusion. It must be clarified whether R-loops lead to replication stress, DNA damage, or transcriptional abnormalities.

7.2 Distinguishing RNase H1 and RNase H2 functions

RNase H1 experiments are more suitable for analyzing long RNA-DNA hybrids and mitochondrial phenotypes. RNase H2 experiments are more suitable for analyzing rNMP incorporation, replication maturation, and innate immune activation. If increased R-loops and DNA damage are observed simultaneously, their contributions should be distinguished according to substrate type, subcellular localization, and the genetic intervention target.

7.3 Sample and cell-cycle control

R-loops and replication stress are strongly affected by the cell cycle. Changes in S-phase proportion, transcription intensity, replication inhibitor treatment, and cytotoxicity can all alter R-loop readouts. Comparisons among treatment groups should ideally be performed under relatively stable conditions for flow cytometric cell-cycle distribution, EdU incorporation, cell viability, and transcription levels.

7.4 Multi-indicator validation

Reliable R-loop research should not depend on a single assay. A basic combination may include DRIP-qPCR, RNase H treatment, S9.6 immunofluorescence, and DNA damage indicators. For deeper mechanistic studies, R-ChIP, DRIP-seq, DNA fiber assays, RNA-seq, ChIP-seq, or cell-state controls can be added.

8 Product Selection for RNA-DNA Hybrid, RNase H, and R-loop Regulation Research

Table 6 Product Selection for RNase H, RNASEH Gene Intervention, and Direct R-loop Processing

Application Module	Cat. No.	Product Name	Grade & Purity	Application Positioning
RNA-DNA hybrid processing	R665576	RNase H	600U	Used to degrade the RNA strand in RNA-DNA hybrids; suitable for DRIP, S9.6 detection, and R-loop signal validation
RNA-DNA hybrid processing	R754998	Ribonuclease H (RNase H)	from Escherichia coli H 560 pol A1	Used for in vitro RNA-DNA hybrid processing and RNase H sensitivity controls
RNA-DNA hybrid processing	T751065	Thermostable RNase H	BioReagent, DNase, RNase free, Suitable for molecular biology, EnzymoPure™, sterile, for DNA and RNA applications, ≥95%, 5 U/μl	Used for RNA-DNA hybrid processing under higher-temperature conditions and reaction system optimization
RNase H2 enzymatic processing	rp224200	RNase HII	ActiBioPure™, EnzymoPure™, Bioactive, Animal Free, Carrier Free, ≥95%(SDS-PAGE), 5.0 U/μL	Used for RNase H2-related RNA-DNA hybrid processing and enzymatic validation
RNase H2 enzymatic processing	T1522666	Thermostable RNase HII	Recombinant, Suitable for molecular biology, EnzymoPure™, ≥95%(SDS-PAGE), expressed in E.coli; 2 U/μl	Used for thermostable RNase HII reaction systems and RNA-DNA hybrid processing
RNase H protein validation	rp329595	Recombinant Human RNASEH Protein	≥90%(SDS-PAGE)	Used as a positive control for RNase H-related assays, antibody validation, or enzymatic system development
RNase H2A protein validation	rp330242	Recombinant Mouse RNASEH2A Protein	≥90%(SDS-PAGE)	Used for RNase H2A protein detection, antibody validation, and methodological controls
RNASEH1 expression intervention	R1472891	RNASEH1 Human Pre-designed siRNA Set A		Used for RNASEH1 knockdown to study nuclear R-loop accumulation, mitochondrial RNA-DNA hybrid processing, and DNA damage changes
RNASEH2A expression intervention	R1489395	RNASEH2A Human Pre-designed siRNA Set A		Used for knockdown of the RNase H2 catalytic subunit to analyze rNMP excision repair, R-loop abnormalities, and replication stress
RNASEH2B expression intervention	R1479915	RNASEH2B Human Pre-designed siRNA Set A		Used for knockdown of an RNase H2 complex subunit to study complex stability, DNA damage, and immune activation
RNASEH2C expression intervention	R1461774	RNASEH2C Human Pre-designed siRNA Set A		Used for RNase H2 complex functional validation and RNASEH2C-dependent phenotype analysis
RNase H2A protein validation	Ab125320	RNASEH2A Mouse mAb	See COA	Used for Western blot, IF, or RNASEH2A expression validation in cell models
RNase H inhibition research	N170153	NSC727447	Moligand™,≥98%	Used for viral RNase H-related enzymatic research; not suitable as a direct substitute for human RNase H1/H2 functional inhibitors
RNase-free system maintenance	R489315	RNase Inhibitor	pharmaceutical grade, PharmPure™, ≥95%, 40U/μl	Used to protect RNA samples and reduce interference from nonspecific RNA degradation in R-loop-related assays
RNase-free system maintenance	R489312	RNase Inhibitor	pharmaceutical grade, PharmPure™, ≥95%, 1000U/μl	Used for DRIP, RNA-DNA hybrid detection, and RNA-related sample pretreatment
RNase-free system maintenance	R350859	RNase Inhibitor (Murine, 40U/μL)	Recombinant, BioReagent, DNase, RNase free, Suitable for molecular biology, for DNA and RNA applications, ≥95%(SDS-PAGE), 40U/μl	Used for RNA protection and RNase contamination control in nucleic acid workflows
RNase-free system maintenance	R292575	RNase Inhibitor（RNasin）	40U/μl	Used for RNA protection during R-loop-related sample preparation

Table 7 Product Selection for R-loop Detection, Nucleic Acid Processing, and Auxiliary Experimental Systems

Application Module	Cat. No.	Product Name	Grade & Purity	Application Positioning
RNase-free aqueous system	R665526	RNase-Free Water	100 ml	Used for DRIP, qPCR, RNA-DNA hybrid processing, and RNase sensitivity experiments
RNase-free buffer system	P743267	PBS, DNase&RNase Free	sterile-filtered, BioReagent, DNase, RNase free, ready-to-use, for cell culture, 1×	Used for cell washing, immunofluorescence, and nucleic acid sample processing
RNase-free electrophoresis system	B1518790	BPTE Running B uffer (10×, RNase Free)	BioReagent,Suitable for molecular biology,RNase free,for NA electrophoresis,10×	Used for RNA or nucleic acid sample electrophoresis while reducing RNase contamination
RNase-free hybridization system	S1518774	SSC Buffer (20×, pH 7.0, RNase Free)	BioReagent,Suitable for molecular biology,RNase free,sterile,for DNA and RNA applications,20×	Used for nucleic acid hybridization, washing, and R-loop-related nucleic acid detection systems
RNase-free hybridization system	S743320	SSPE	20X, pH7.4	Used for nucleic acid hybridization and high-cleanliness nucleic acid workflows
RNase-free electrophoresis system	T1518779	TAE Buffer (50×, RNase Free)	BioReagent,Suitable for molecular biology,for NA electrophoresis,RNase free,50×	Used for nucleic acid fragment analysis and DRIP sample quality assessment
RNase-free electrophoresis system	T1518783	TBE Buffer (5×, RNase Free)	BioReagent,Suitable for molecular biology,RNase free,for NA electrophoresis,5×	Used for DNA/RNA-related electrophoretic detection
Nucleic acid extraction system	C1518317	CTAB Extraction Buffer (RNase free)	BioReagent,Suitable for molecular biology	Used for nucleic acid sample extraction, suitable for sample pretreatment requiring RNase contamination control
Sample precipitation/enrichment	P748949	PEG8000 (50%, RNase free)	BioReagent, DNase, RNase free, Protease Free, ≥99%, 50%	Used for nucleic acid precipitation, enrichment, or molecular biology reaction optimization
RNase contamination removal	R666126	RNase and DNA Remover	250ml	Used to control RNase/DNA contamination on work surfaces, consumables, or instruments
dsRNA background control	R749972	RNase III (dsRNA-specific)	ActiBioPure™, EnzymoPure™, Bioactive, Animal Free, Carrier Free, sterile, DNase free, 2.0 U/µL	Used to distinguish dsRNA background from RNA-DNA hybrid signals in S9.6-based detection
ssRNA background control	R128619	Ribonuclease A from bovine pancreas(DNase & Protease Free)	Bioactive,ActiBioPure™,Native,High Performance,EnzymoPure™,DNase free,Protease Free,≥2,000 units/mg protein	Used for removal of non-hybrid RNA or nucleic acid specificity controls; should be used carefully to avoid disrupting the target detection system
ssRNA background control	R665518	RNase A	EnzymoPure™, DNase free, Protease Free, sterile, ≥90%(SDS-PAGE), 10 mg/mL	Used for RNA background control and optimization of nucleic acid processing conditions
DNA background control	R1373644	Recombinant DNase I, RNase-free	EnzymoPure™, ≥95%(SDS-PAGE), 1 U/μl	Used for removal of DNA contamination in RNA samples or DNA-dependent signal controls
DNA background control	D755003	Deoxyribonuclease I bovine	Recombinant, expressed in Pichia pastoris, buffered aqueous glycerol solution,≥5,000 units/mg protein	Used for DNA digestion and nucleic acid specificity control experiments
Cell plating/immunodetection	P1508964	Poly-L-lysine Solution (1×, 0.1 mg/mL, RNase free, Sterile)	BioReagent,for microscopy,for cell culture,RNase free,sterile,Suitable for Immunohistochemistry(IHC),1×, 0.1 mg/mL	Used for cell coverslip experiments such as S9.6 immunofluorescence and DNA damage foci detection

Table 8 Product Selection for R-loop-Related Replication Stress, DNA Damage, and cGAS-STING Pathway Research

Application Module	Cat. No.	Product Name	Grade & Purity	Application Positioning
DNA damage marker research	H1490350	H2AX Human Pre-designed siRNA Set A		Used for H2AX functional intervention to support analysis of R-loop-related DNA damage responses
DNA damage marker research	rp156659	Recombinant Human Histone H2AX Protein	Carrier Free,Azide Free,His Tag,≥90%(SDS-PAGE)	Used for H2AX-related antibody validation, positive controls, and DNA damage detection system development
DNA double-strand break response	Ab086721	53BP1 Antibody	ExactAb™, Validated, 0.5 mg/mL	Used for detecting R-loop-related DNA damage foci and double-strand break responses
DNA double-strand break response	T1489652	TP53BP1 Human Pre-designed siRNA Set A		Used for TP53BP1 knockdown to validate 53BP1-dependent DNA damage repair phenotypes
DNA double-strand break response	Ab326127	TP53BP1 Mouse mAb	Skip to the end of the images gallery 3D Skip to the beginning of the images gallery KD Validation	Used for TP53BP1 protein expression and damage foci detection
DNA double-strand break response	P751196	pLenti-TP53BP1-sgRNA		Used for TP53BP1 antibody validation and negative controls
DNA double-strand break response	P751197	pLenti-TP53BP1-sgRNA		Used as a negative control for TP53BP1 transcription detection
DNA damage quantification	EJ1514690	Human Tumor Protein p53 Binding Protein 1 (TP53BP1) ELISA Kit	BioReagent	Used for detecting TP53BP1 levels in human samples and supporting evaluation of DNA damage responses
Replication stress/ssDNA exposure	Ab125728	RPA32/RPA2 Mouse mAb	ExactAb™, Validated, Carrier Free, High performance, 0.5 mg/mL	Used for detecting replication fork stalling, ssDNA exposure, and replication stress
Replication stress/ssDNA exposure	Ab125724	Recombinant RPA32/RPA2 Antibody	Recombinant, ExactAb™, Validated, See COA	Used for replication stress and R-loop-related RPA foci detection
cGAS pathway intervention	C1475161	CGAS Human Pre-designed siRNA Set A		Used for cGAS knockdown in human cells to validate cytosolic DNA sensing triggered by RNase H2 deficiency or DNA damage
cGAS pathway intervention	C1465684	Cgas Mouse Pre-designed siRNA Set A		Used for cGAS knockdown in mouse models to analyze innate immune activation related to abnormal nucleic acid metabolism
cGAS pathway intervention	C1476069	Cgas Rat Pre-designed siRNA Set A		Used for cGAS knockdown and pathway validation in rat-derived cells
cGAS functional regulation	C1497613	cGAS-IN-1	Moligand™, 10 mM in DMSO	Used to inhibit cGAS activity and validate the role of the cytosolic DNA-cGAS axis in R-loop/RNase H2-deficient phenotypes
cGAS functional regulation	C1434281	cGAS-IN-2	≥99%	Used for cGAS pathway inhibition and dose-response studies
cGAS functional regulation	C1434284	cGAS-IN-4		Used to validate cGAS-mediated innate immune activation
cGAS quantitative detection	EJ1513959	Human Mab21 Domain Containing Protein 1 (MB21D1/CGAS) ELISA Kit	BioReagent	Used for detecting cGAS/MB21D1 levels in human samples
cGAS quantitative detection	EJ1512722	Mouse Mab21 Domain Containing Protein 1 (MB21D1/CGAS) ELISA Kit	BioReagent	Used for detecting cGAS/MB21D1 in mouse samples
STING pathway validation	Ab129563	Recombinant STING Antibody	ExactAb™, Validated, Recombinant, 0.4 mg/mL	Used for STING protein expression and cGAS-STING pathway activation detection
STING expression intervention	S1487331	STING1 Human Pre-designed siRNA Set A		Used for STING1 knockdown in human cells to validate immune phenotypes related to R-loop/RNase H2 deficiency
STING expression intervention	S1490953	Sting1 Mouse Pre-designed siRNA Set A		Used for Sting1 knockdown and innate immune pathway validation in mouse models
STING expression intervention	S1470688	Sting1 Rat Pre-designed siRNA Set A		Used for STING pathway intervention in rat-derived models
STING inhibition	C408221	C-176 (STING inhibitor)	10mM in DMSO	Used to inhibit the STING pathway and validate immune activation dependence after DNA damage or cytosolic DNA accumulation
STING inhibition	H287635	H 151	Moligand™, ≥98%(HPLC)	Used for STING pathway inhibition and innate immune response rescue experiments
STING activation	C413869	cGAMP sodium salt	≥99%	Used as a positive activation control for the STING pathway
STING activation	D646335	diABZI STING agonist-1	≥99%	Used as a positive control for STING pathway activation and pathway sensitivity validation
STING activation	M288436	MSA 2	Moligand™,≥98%(HPLC)	Used for non-nucleotide STING activation research
STING quantitative detection	EJ1514083	Human Stimulator of interferon genes (STING) ELISA Kit	BioReagent	Used for detecting STING levels in human samples
Interferon-stimulated gene detection	I1472959	ISG15 Human Pre-designed siRNA Set A		Used for ISG15 knockdown to analyze ISG responses after RNase H2 deficiency or cGAS-STING activation
Interferon-stimulated gene detection	Ab111307	Recombinant ISG15 Antibody	Recombinant, ExactAb™, Validated, High Performance, See COA	Used for ISG15 protein expression detection and interferon response validation
Interferon-stimulated gene detection	Ab326649	Recombinant ISG15 Antibody	3D Skip to the beginning of the images gallery KD Validation	Used for ISG15 expression validation and immunodetection
Interferon-stimulated gene detection	EJ1514492	Human Ubiquitin-like Modifier (ISG15) ELISA Kit	BioReagent	Used for quantifying ISG15 in human samples and evaluating innate immune activation
Interferon-stimulated gene detection	EJ1512845	Mouse Ubiquitin-like Protein ISG15 (ISG15) ELISA Kit	BioReagent	Used for ISG15 detection and interferon response analysis in mouse models

9 Common Questions

9.1 Are RNA-DNA hybrids and R-loops the same concept?

Not exactly. RNA-DNA hybrids broadly refer to structures formed by pairing between RNA and DNA strands. R-loops usually refer to three-stranded nucleic acid structures in which an RNA-DNA hybrid is accompanied by displacement of one DNA strand. All R-loops contain RNA-DNA hybrids, but not all RNA-DNA hybrids constitute typical R-loops.

9.2 Which is more suitable for clearing R-loops, RNase H1 or RNase H2?

RNase H1 is more commonly used to clear relatively long RNA-DNA hybrids and validate R-loop signals. RNase H2 can also process some hybrids, but its key function also includes recognizing and removing single ribonucleotides in DNA. The two enzymes should not be considered simple substitutes for each other.

9.3 Why does RNase H2 deficiency affect genome stability?

RNase H2 deficiency prevents proper removal of ribonucleotides embedded in DNA and may be accompanied by replication stress, DNA breaks, R-loop abnormalities, and innate immune activation. Its phenotype is usually more complex than simple R-loop accumulation.

9.4 Is S9.6 antibody detection of R-loops reliable?

S9.6 is a commonly used tool, but RNase H treatment controls are required. If the signal is RNase H-sensitive, it is more likely to originate from RNA-DNA hybrids. If it is not sensitive, double-stranded RNA or nonspecific background should be considered.

9.5 Do R-loops always cause DNA damage?

No. Some R-loops have normal regulatory functions. They are more likely to cause replication stress and DNA damage only when they form excessively, are not efficiently cleared, occur at abnormal locations, or conflict with replication forks. Interpretation should be combined with DNA damage and replication indicators.

9.6 How can one prove that a DNA damage phenotype is caused by R-loops?

It is necessary to demonstrate consistency among increased R-loops, elevated damage markers, and RNase H-dependent rescue. Common designs include DRIP-qPCR localization, RNase H1 overexpression rescue, catalytically inactive controls, DNA fiber assays for replication stress, and γH2AX/53BP1 damage validation.

9.7 What should be considered in mitochondrial R-loop research?

Mitochondrial RNA-DNA hybrids are closely related to mtDNA replication and transcription. RNase H1, mtDNA copy number, mitochondrial transcription, respiratory chain function, and mitochondrial DNA damage should be detected. Nuclear R-loop detection methods should not be used directly as substitutes.

RNA-DNA hybrids are important structures at the intersection of gene expression, replication, and repair. RNase H1 preferentially processes relatively long hybrids and mitochondrial-associated structures, whereas RNase H2 connects rNMP excision repair, replication maturation, and immune homeostasis. Only by jointly analyzing R-loop localization, RNase H function, replication stress, and DNA damage readouts can the role of RNA-DNA hybrids in genome stability be accurately determined.