2-Thiouracil (2TU): Properties, Applications & Lab Guidelines

2-Thiouracil(2TU) is a sulfur-substituted uracil analog widely used in metabolic RNA labeling experiments and thyroid hormone biosynthesis research due to its selective incorporation into nascent RNA and its ability to inhibit iodination of thyroglobulin.

Chemical Name

2-Thiouracil (2-thio-2,4(1H,3H)-pyrimidinedione)

Molecular Formula

C₄H₄N₂OS

Molecular Weight

128.15 g/mol

CAS Number

141-90-2

Primary Application

Metabolic RNA pulse-labeling; thyroid hormone synthesis inhibition

Recommended Storage

Room temperature, protected from light and moisture

Chemical Identity and Physical Properties

2-Thiouracil (2TU) is a naturally occurring and synthetically produced pyrimidine analog in which the oxygen at the C2 position of uracil is replaced by a sulfur atom. Its IUPAC name is 2-thioxo-2,3-dihydropyrimidin-4(1H)-one, CAS 141-90-2, with the molecular formula C₄H₄N₂OS and a molecular weight of approximately 128.15 g/mol.

2TU typically appears as a white to off-white crystalline powder. It has limited solubility in water at room temperature but dissolves more readily in dilute alkali solutions. The compound exhibits UV absorbance characteristic of thiated pyrimidines, which underpins its use in thiol-reactive chemistries. The thiol tautomer at C2 confers nucleophilic reactivity that enables bioorthogonal conjugation reactions, such as biotinylation following iodoacetyl or maleimide chemistry after metabolic incorporation into RNA.

Mechanisms of Action and Biological Significance

2TU exerts its biological effects through two principal mechanisms depending on experimental context:

1. Metabolic RNA labeling: When supplied to cells, 2TU is incorporated by RNA polymerases into nascent RNA transcripts in place of uracil. The resulting thio-substituted transcripts can subsequently be selectively captured or detected using thiol-reactive reagents such as MTSEA-biotin or iodoacetamide-biotin. This approach, often called thiol-linked alkylation for the metabolic sequencing of RNA (SLAM-seq) or related pulse-labeling strategies, enables time-resolved transcriptomics by distinguishing newly synthesized RNA from pre-existing transcripts without physical separation of cell populations.

2. Inhibition of thyroid hormone biosynthesis: 2TU inhibits the enzyme thyroid peroxidase, thereby blocking the iodination of thyroglobulin and the coupling reactions required for thyroxine (T4) and triiodothyronine (T3) synthesis. This pharmacological property has made 2TU a classical antithyroid tool compound in biochemical and endocrinological research.

Recommended Protocols and Handling Guidelines

Stock solution preparation: Prepare a concentrated stock solution (e.g., 100–200 mM) by dissolving 2TU in phosphate-buffered saline (PBS) adjusted to pH 7.4–8.0 or in DMSO. Gentle warming (37 °C) and vortexing may aid dissolution. Filter-sterilize if the solution will be used in cell culture.

Cell culture pulse-labeling: Add 2TU to culture medium at a working concentration typically in the range of 100 µM to 1 mM, depending on cell type and duration of labeling. Incubate for the desired pulse period (commonly 1–24 h). Following labeling, wash cells with fresh medium to remove unincorporated 2TU before RNA extraction.

RNA extraction and thiol biotinylation: Extract total RNA using a standard acid-guanidinium-phenol-chloroform or spin-column method. React the thio-labeled RNA with a thiol-reactive biotin reagent according to the reagent manufacturer's protocol. Streptavidin-based pulldown then enables enrichment of newly synthesized transcripts for downstream sequencing or qPCR analysis.

Storage: Store the solid reagent at room temperature in a tightly sealed container, protected from light and moisture. Prepared stock solutions should be aliquoted and stored at −20 °C to avoid repeated freeze–thaw cycles.

Safety and Regulatory Considerations

2TU should be handled as a potentially hazardous chemical in accordance with standard laboratory safety practices. Key precautions include:

• Personal protective equipment (PPE): Wear appropriate gloves, laboratory coat, and eye protection when handling the solid or solution forms.
• Inhalation and ingestion: Avoid generating dust. Do not pipette by mouth. Work in a well-ventilated area or fume hood when handling large quantities or preparing concentrated solutions.
• Antithyroid activity: Chronic or high-dose exposure may interfere with thyroid function. This is particularly relevant for pregnant women or individuals with known thyroid disorders.
• Waste disposal: Dispose of 2TU-containing waste according to your institutional chemical waste management procedures and applicable local regulations.
• SDS: Always consult the Safety Data Sheet (SDS) supplied by Aladdin Scientific before use. Specific hazard classifications, first-aid measures, and disposal codes are detailed therein.

This reagent is intended for research use only and is not approved for diagnostic, therapeutic, or food use.

Quality, Purity, and Ordering Information

Aladdin Scientific's 2-Thiouracil (2TU), SKU T106705, is manufactured to research-grade purity standards. Purity is verified by HPLC and/or NMR prior to release. Lot-specific certificates of analysis (CoA) are available upon request and via the product page on the Aladdin Scientific website.

Researchers requiring the highest levels of consistency across experimental batches are encouraged to record the lot number used in publications and to contact Aladdin Scientific's technical support team for batch-reservation options on larger projects. Custom quantities and bulk pricing may be available; contact your local Aladdin Scientific representative or submit an inquiry through the website for details.

For questions regarding specification, grade, or purity requirements for specific applications, please contact Aladdin Scientific technical support.

Frequently asked questions

What concentration of 2-Thiouracil should I use for metabolic RNA labeling in mammalian cell culture?

Working concentrations of 100 µM to 1 mM are commonly reported for mammalian cells, with 200–500 µM being a frequently used starting point. The optimal concentration depends on the cell type, metabolic activity, and labeling duration; pilot experiments assessing incorporation efficiency and cell viability are recommended before committing to a full experimental design.

How does 2-Thiouracil differ from 4-Thiouridine (4SU) in RNA labeling applications?

4-Thiouridine (4SU) is a nucleoside that is directly phosphorylated intracellularly and incorporated into RNA; it is the more widely used reagent for metabolic RNA labeling via SLAM-seq and related methods. 2-Thiouracil (2TU), a nucleobase without the ribose moiety, requires conversion to the nucleotide form by cellular salvage pathways before incorporation and may show different uptake and incorporation efficiencies depending on the organism or cell line. Researchers should validate incorporation for their specific system when substituting one reagent for the other.

Can 2-Thiouracil be used in model organisms such as yeast or C. elegans?

Yes, 2TU has been used for metabolic RNA labeling in organisms including yeast and C. elegans, often in conjunction with uracil phosphoribosyltransferase (UPRT) expression to enhance nucleotide salvage and incorporation. The specific experimental conditions, including concentration and labeling duration, must be optimized for each organism. Consulting primary literature for your model organism of interest is strongly advised.

How should I store the 2-Thiouracil stock solution to maintain stability?

Prepared stock solutions should be aliquoted into single-use volumes and stored at −20 °C, protected from light. Repeated freeze–thaw cycles should be avoided as they can degrade the compound over time. The solid reagent itself is stable at room temperature when kept dry and away from light.

References

1. Dolken L et al. High-resolution gene expression profiling for simultaneous kinetic parameter analysis of RNA synthesis and decay. RNA. 2008.
2. Muhar M et al. SLAM-seq defines direct gene-regulatory functions of the BRD4-MYC axis. Science. 2018.
3. Duffy EE et al. Tracking distinct RNA populations using efficient and reversible covalent chemistry. Molecular Cell. 2015.
4. Astrom A and Bohman R. Thyroid peroxidase inhibition by thiouracil derivatives. Biochemical Pharmacology. 1967.

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.