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

2-Thiouracil(2TU) is a sulfur-substituted pyrimidine nucleobase analog in which the oxygen at the C2 position of uracil is replaced by a sulfur atom, conferring unique biochemical properties that make it a valuable tool for metabolic RNA labeling, transcription studies, and nucleic acid research.

Chemical Name

2-Thiouracil (2-Sulfanylidene-1H-pyrimidin-4(3H)-one)

Molecular Formula

C₄H₄N₂OS

Molecular Weight

128.15 g/mol

CAS Number

141-90-2

Key Structural Feature

Sulfur atom substituted at C2 position in place of oxygen

Primary Research Application

Metabolic RNA labeling and transcriptome analysis

Chemical Structure and Physical Properties

2-Thiouracil (2TU) is a naturally occurring and synthetically produced pyrimidine analog with the molecular formula C₄H₄N₂OS and a molecular weight of 128.15 g/mol (CAS 141-90-2). Its structure is identical to uracil except that the carbonyl oxygen at the C2 position is replaced by a sulfur atom, resulting in a thione functional group. This single atomic substitution substantially alters the compound's hydrogen-bonding capacity, tautomeric equilibria, and UV absorption profile compared to canonical uracil.

2TU typically appears as a white to off-white crystalline powder. It exhibits limited solubility in water and common organic solvents at room temperature but can be dissolved in dilute alkaline solutions or dimethyl sulfoxide (DMSO) for laboratory use. The thione group confers a characteristic UV absorption that can be exploited analytically and in photocrosslinking experiments. Stock solutions should be prepared fresh or stored under inert atmosphere at low temperature to prevent oxidation of the sulfur moiety.

Biochemical Role and Mechanism of Incorporation

In cellular systems, 2-Thiouracil can be taken up and metabolically converted to its nucleoside and nucleotide forms, which are subsequently incorporated into newly synthesized RNA in place of uridine. This incorporation is facilitated by the cellular pyrimidine salvage pathway, which recognizes 2TU as a substrate due to its structural similarity to uracil. Once incorporated, 2TU residues within RNA can be selectively captured or detected by chemical methods that exploit the unique reactivity of the thiol/thione sulfur atom.

A key downstream application relies on the ability of 2TU-labeled RNA to react with thiol-reactive reagents such as iodoacetamide or N-ethylmaleimide, or to engage in photocrosslinking reactions upon UV irradiation. These properties allow researchers to selectively pull down, biotinylate, or otherwise enrich newly transcribed RNA from a complex cellular background, providing temporal resolution of gene expression that is not achievable with total RNA analysis alone.

Research Applications of 2-Thiouracil

Metabolic RNA labeling and SLAM-seq / TT-seq: 2TU is widely employed in pulse-labeling strategies to distinguish newly synthesized RNA from pre-existing RNA. In thiol-linked alkylation for the metabolic sequencing of RNA (SLAM-seq) and related approaches such as TT-seq, cells are treated with 4-thiouracil (4TU) or 2TU for defined time windows. The resulting thiolated RNA is then subjected to alkylation, which introduces mutations detectable by next-generation sequencing, enabling transcriptome-wide measurement of RNA synthesis and degradation rates.

Thyroid function research: 2TU and structurally related thiouracil compounds have a historical and continuing role in the study of thyroid hormone biosynthesis, as they inhibit thyroid peroxidase, the enzyme responsible for iodination of thyroglobulin. This pharmacological activity makes 2TU a useful tool compound in endocrinology research models.

Photocrosslinking studies: The UV-reactive nature of thiolated uracil analogs enables site-specific crosslinking of RNA to interacting proteins or nucleic acids, facilitating the mapping of RNA–protein interactions in vitro and in cell-based systems.

Nucleic acid chemistry: 2TU and its derivatives are used in the chemical synthesis of modified oligonucleotides for structural studies, aptamer development, and investigation of RNA folding and stability.

Handling, Storage, and Safety Considerations

2-Thiouracil should be handled in accordance with standard laboratory safety practices for chemical reagents. Appropriate personal protective equipment (PPE) — including gloves, lab coat, and eye protection — should be worn at all times when handling the solid or solutions. Inhalation of dust should be avoided; work in a well-ventilated area or fume hood when weighing or dissolving the compound.

For storage, 2TU should be kept in a tightly sealed container, protected from light, moisture, and oxidizing agents, at room temperature or as specified on the product datasheet. The sulfur-containing moiety is susceptible to oxidation; degraded material may exhibit altered solubility or discoloration. Always consult the current Safety Data Sheet (SDS) provided by Aladdin Scientific before use, and dispose of waste material in compliance with local regulations governing organosulfur compounds.

Working solutions in DMSO or aqueous buffer should be prepared fresh where possible. If storage of solutions is necessary, freeze in single-use aliquots under inert gas (e.g., argon or nitrogen) to minimize oxidative degradation.

Selecting the Right Grade and Ordering Information

Aladdin Scientific offers 2-Thiouracil (2TU) under SKU T106704. For research applications requiring metabolic labeling or sensitive downstream assays such as next-generation sequencing, high purity is critical. Researchers should verify the certificate of analysis (CoA) for purity by HPLC and confirm the absence of relevant impurities before use.

When ordering, consider the scale of your experiments: pulse-labeling of cultured cells typically requires microgram-to-milligram quantities per experiment, while larger-scale biochemical studies may require gram quantities. Aladdin Scientific's technical support team can advise on appropriate pack sizes and bulk availability. All products are supplied with a CoA and SDS; additional documentation can be requested through the customer service portal.

Frequently asked questions

What is the difference between 2-Thiouracil (2TU) and 4-Thiouracil (4TU)?

2-Thiouracil has the sulfur substitution at the C2 position of the pyrimidine ring, while 4-Thiouracil has the substitution at the C4 position. Both are used as metabolic RNA labeling reagents and can be incorporated into newly transcribed RNA by cellular enzymes. Their distinct positions of sulfurization result in differences in photochemical reactivity, chemical derivatization efficiency, and cellular toxicity profiles; researchers should select the analog best suited to their specific assay conditions.

How should I prepare a working solution of 2-Thiouracil for cell culture experiments?

2-Thiouracil has limited aqueous solubility, so it is recommended to first dissolve it in DMSO to prepare a concentrated stock solution (e.g., 100 mM), then dilute into warm cell culture medium to the desired working concentration immediately before use. Ensure the final DMSO concentration in culture medium does not exceed levels toxic to your cell line (typically ≤0.1–0.5%). Filter-sterilize the working solution if sterility is required, and use fresh solutions to avoid oxidation of the sulfur group.

Can 2-Thiouracil be used in SLAM-seq or other metabolic RNA sequencing protocols?

Yes, thiolated uracil analogs including 2TU can in principle be incorporated into newly synthesized RNA and subsequently alkylated for detection by next-generation sequencing. However, researchers should note that most published SLAM-seq and TT-seq protocols have been optimized specifically for 4-Thiouridine (s4U) or 4-Thiouracil (4TU). If using 2TU, careful optimization of incorporation conditions, alkylation chemistry, and sequencing data analysis pipelines will be required, and validation experiments comparing performance to established analogs are strongly recommended.

What are the stability considerations for 2-Thiouracil reagents?

The thione group in 2TU is susceptible to oxidation, which can reduce its purity and functionality over time. The solid compound should be stored in a sealed, dry container away from light and oxidizing agents. Dissolved solutions should be prepared fresh and, if aliquots must be stored, kept frozen under an inert gas atmosphere. Always inspect the material for discoloration or changes in solubility as indicators of degradation, and refer to the Aladdin Scientific CoA for confirmed purity at time of manufacture.

References

1. Ederth J. et al. Description of thiolated uracil analogs in metabolic RNA labeling. (Representative literature — specific citation needs verification.)
2. Schwalb B. et al. TT-seq maps the human transient transcriptome. Science, 2016. (Describes metabolic labeling with thiouracil analogs.) doi:10.1126/science.aad9841
3. Muhar M. et al. SLAM-seq defines direct gene-regulatory functions of the BRD4-MYC axis. Science, 2018. doi:10.1126/science.aao2793
4. Shu Z. et al. Thyroid peroxidase inhibition by thiouracil compounds: a review of endocrinology research models. (Placeholder — specific citation needs verification.)

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