GO:0016427 tRNA (cytidine) methyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0016427 describes the enzymatic activity that transfers a methyl group from S-adenosyl-L-methionine (SAM) to cytidine residues in tRNA, producing S-adenosyl-L-homocysteine and methylcytosine-containing tRNA.
• This activity is essential for tRNA stability, decoding fidelity, and translational efficiency, and it is conserved from bacteria to humans.
• Key enzymes include Dnmt2 (TRDMT1) in eukaryotes and METTL6 in mammals, which catalyze m5C and m3C modifications, respectively.
• Dysregulation of tRNA cytidine methylation is linked to cancer, neurological disorders, and immune dysfunction.
• CRISPR-based knockout, point-mutation, and knock-in models are powerful tools to dissect the function of these methyltransferases.
• EDITGENE provides comprehensive CRISPR services to study tRNA (cytidine) methyltransferase activity and its role in disease.
Description
tRNA (cytidine) methyltransferase activity (GO:0016427) is a molecular function that catalyzes the methylation of cytidine residues in transfer RNA (tRNA) using S-adenosyl-L-methionine (SAM) as the methyl donor. This modification, typically forming 5-methylcytosine (m5C) or 3-methylcytosine (m3C), is critical for tRNA structure, stability, and function in protein synthesis. The activity is conserved across all domains of life and is carried out by enzymes such as Dnmt2 (TRDMT1) in eukaryotes and METTL6 in mammals. Researchers study this activity to understand its roles in translation regulation, cellular stress responses, and disease pathogenesis. The precise mapping of methylation sites and the enzymes responsible has been advanced by chemoproteomic and structural approaches.
tRNA (cytidine) methyltransferase activity At A Glance
| GO ID | GO:0016427 |
|---|---|
| GO term | tRNA (cytidine) methyltransferase activity |
| Ontology | molecular_function |
| Synonym | tRNA (cytosine) methyltransferase activity |
| Major function | Methylation of cytidine in tRNA using SAM |
| Reaction | S-adenosyl-L-methionine + tRNA = S-adenosyl-L-homocysteine + tRNA containing methylcytosine |
| Cofactor | S-adenosyl-L-methionine (SAM) |
| Localization | Nucleus and cytoplasm (varies by enzyme) |
| Representative enzymes | Dnmt2 (TRDMT1), METTL6, NSUN2, NSUN6 |
What Is GO:0016427?
GO:0016427 is defined as the catalysis of the reaction: S-adenosyl-L-methionine + tRNA = S-adenosyl-L-homocysteine + tRNA containing methylcytosine. In other words, it is the enzyme activity that adds a methyl group to a cytidine nucleotide within a tRNA molecule, using SAM as the methyl donor and releasing SAH.
Why Is tRNA (cytidine) methyltransferase activity Important in Cell Biology?
tRNA (cytidine) methyltransferase activity is crucial for maintaining the fidelity and efficiency of protein synthesis. Methylation of cytidine residues in tRNA affects tRNA folding, stability, and codon-anticodon interactions, thereby influencing translation rates and accuracy. Dysregulation of this activity has been implicated in various human diseases, including cancer, where altered tRNA methylation can promote tumorigenesis. Additionally, these modifications play roles in immune responses and neurological functions. Understanding this activity provides insights into fundamental cellular processes and potential therapeutic targets.
• Ensures proper tRNA folding and stability, which is essential for efficient translation.
• Modulates codon-anticodon pairing and translational fidelity.
• Influences cell proliferation and differentiation through translational control.
• Linked to cancer development and progression via epigenetic dysregulation.
• Plays a role in immune cell function and IgA nephropathy.
• Potential biomarker for disease diagnosis and prognosis.
• Target for therapeutic intervention in cancers and genetic disorders.
• Conserved across species, facilitating model organism studies.
• Involved in stress response and adaptation.
• Subject to regulation by metabolic and signaling pathways.
Molecular Mechanism of tRNA (cytidine) methyltransferase activity
Substrate Recognition and Binding
In simple terms: The enzyme finds and grabs the specific tRNA it needs to modify.
tRNA (cytidine) methyltransferases recognize their substrate tRNAs through specific structural features, including the anticodon loop and overall L-shaped fold. For example, Dnmt2 binds tRNAAsp and methylates C38, while METTL6 targets tRNASer and modifies C32. The binding is often guided by sequence motifs and post-transcriptional modifications in the tRNA.
Catalytic Methyl Transfer
In simple terms: The enzyme transfers a methyl group from SAM to the cytidine base.
Once bound, the enzyme positions the target cytidine in its active site and transfers a methyl group from S-adenosyl-L-methionine (SAM) to the C5 or C3 position of the cytosine ring, forming m5C or m3C, respectively. This reaction releases S-adenosyl-L-homocysteine (SAH). The catalytic mechanism involves a conserved cysteine or other residues that activate the cytosine for nucleophilic attack.
Product Release and tRNA Maturation
In simple terms: After modification, the tRNA is released and continues its journey to become functional.
Following methylation, the modified tRNA is released from the enzyme. The methyl group can affect tRNA stability, folding, and interaction with the ribosome. For instance, m5C in tRNA promotes structural stability and prevents degradation. The modified tRNA then participates in translation, where it ensures accurate codon recognition.
Regulation and Cofactor Availability
In simple terms: The enzyme's activity depends on the availability of SAM and can be regulated by cellular signals.
The activity of tRNA (cytidine) methyltransferases is influenced by the intracellular concentration of SAM, which is sensitive to metabolic status. Additionally, post-translational modifications and interacting proteins can modulate enzyme activity. For example, NSUN2 and NSUN6, which also methylate cytidine in RNA, are regulated in a cell-cycle-dependent manner.
Key Genes Involved in GO:0016427 tRNA (cytidine) methyltransferase activity
The following genes encode enzymes with tRNA (cytidine) methyltransferase activity or related RNA methyltransferases that modify cytidine in tRNA.
| Gene | Major Role | Research Relevance |
|---|---|---|
| TRDMT1 (Dnmt2) | Methylates C38 in tRNAAsp, tRNAGly, tRNAVal | Conserved eukaryotic enzyme; role in stress response and development |
| METTL6 | Methylates C32 in tRNASer | m3C modification; linked to cancer and stem cell function |
| NSUN2 | Methylates C34, C40, C48, C49 in various tRNAs | m5C modification; implicated in cancer and neurological disorders |
| NSUN6 | Methylates C72 in tRNAThr and tRNACys | m5C modification; involved in translation regulation |
| NSUN3 | Methylates C32 in mitochondrial tRNAMet | Mitochondrial translation; mutations cause disease |
| NSUN4 | Methylates C911 in mitochondrial 12S rRNA | Mitochondrial ribosome assembly |
| NSUN5 | Methylates C3782 in 28S rRNA | Ribosome function; linked to aging |
| NSUN7 | Methylates C in tRNA and mRNA | Sperm function and fertility |
| DNMT1 | DNA methyltransferase, also methylates tRNA | Epigenetic regulation; cancer |
| DNMT3A | DNA methyltransferase, also methylates tRNA | Epigenetic regulation; cancer |
| DNMT3B | DNA methyltransferase, also methylates tRNA | Epigenetic regulation; cancer |
| ALKBH1 | Demethylates m3C in tRNA | tRNA demethylation; stress response |
| FTO | Demethylates m6A in tRNA | Obesity and cancer |
| METTL3 | Methylates m6A in mRNA and tRNA | Epigenetic regulation; cancer |
| METTL14 | Methylates m6A in mRNA and tRNA | Epigenetic regulation; cancer |
| WTAP | Regulatory subunit of m6A methyltransferase complex | m6A modification; cancer |
| VIRMA | Regulatory subunit of m6A methyltransferase complex | m6A modification; cancer |
| ZC3H13 | Regulatory subunit of m6A methyltransferase complex | m6A modification; cancer |
How Is tRNA (cytidine) methyltransferase activity Regulated?
The activity of tRNA (cytidine) methyltransferases is regulated at multiple levels. Expression of the enzymes can be controlled transcriptionally and post-transcriptionally in response to cellular stress, growth signals, and metabolic status. For instance, NSUN2 is phosphorylated by Aurora B kinase, which affects its localization and activity during mitosis. Additionally, the availability of the methyl donor SAM, which is influenced by diet and metabolism, can directly impact methylation rates. Furthermore, demethylases such as ALKBH1 can reverse m3C modifications, providing a dynamic regulation of tRNA methylation.
tRNA (cytidine) methyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| NSUN2 | Intellectual disability, cancer | NSUN2 knockout mice, patient-derived iPSCs |
| METTL6 | Hepatocellular carcinoma, breast cancer | METTL6 knockout cell lines, xenograft models |
| TRDMT1 (Dnmt2) | Cancer, stress response | Dnmt2 knockout mice, Drosophila models |
| NSUN3 | Mitochondrial encephalopathy | NSUN3 knockout cells, patient fibroblasts |
| NSUN6 | Cancer, translation regulation | NSUN6 knockout cell lines, zebrafish models |
Cancer
Dysregulation of tRNA (cytidine) methyltransferases is frequently observed in cancers. Overexpression of NSUN2 and METTL6 has been reported in various tumors, including breast, colorectal, and liver cancers, where they promote proliferation and metastasis. Conversely, loss of TRDMT1 (Dnmt2) is associated with increased genomic instability and tumor progression. These enzymes are considered potential therapeutic targets.
Neurological Disorders
Mutations in NSUN2 cause intellectual disability and Dubowitz-like syndrome, characterized by microcephaly and developmental delay. NSUN3 mutations lead to mitochondrial dysfunction and encephalopathy. These findings highlight the critical role of tRNA methylation in neuronal development and function.
Immune Dysfunction
tRNA methylation influences immune cell differentiation and function. In IgA nephropathy, 5-azacytidine treatment modulates B-cell epigenetic programs, including tRNA methylation, affecting IgA production. This suggests a role for tRNA (cytidine) methyltransferases in autoimmune and inflammatory diseases.
From tRNA (cytidine) methyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of NSUN2 knockout on tRNA methylation and translation? | NSUN2 knockout HEK293 cells |
| How does METTL6 point mutation affect m3C modification and cancer cell growth? | METTL6 point-mutant knock-in Huh7 cells |
| Does TRDMT1 overexpression alter stress response? | TRDMT1 overexpression in HeLa cells |
| What is the impact of NSUN3 knockout on mitochondrial translation? | NSUN3 knockout HeLa cells |
| Can NSUN6 be tagged for localization studies? | NSUN6 knock-in with GFP tag in U2OS cells |
| What is the role of Dnmt2 in development? | Dnmt2 knockout mouse model |
How to Study the tRNA (cytidine) methyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| RNA bisulfite sequencing | m5C sites in tRNA | Mapping methylation sites at single-base resolution |
| LC-MS/MS | Modified nucleoside levels | Quantifying m5C and m3C stoichiometry |
| Ribo-seq | Translation efficiency and ribosome pausing | Assessing impact of tRNA methylation on translation |
| CRISPR knockout | Gene function loss | Studying phenotypic effects of methyltransferase deletion |
| CRISPR knock-in | Tagged or mutant protein expression | Localization and interaction studies |
| CLIP-seq | RNA binding sites of enzymes | Identifying tRNA targets of methyltransferases |
| In vitro methylation assay | Enzymatic activity | Measuring methyltransferase activity with recombinant enzymes |
RNA Bisulfite Sequencing
RNA bisulfite sequencing allows genome-wide detection of m5C modifications in tRNA at single-base resolution. It involves treating RNA with bisulfite, which converts unmethylated cytosine to uracil, while methylated cytosine remains unchanged. After sequencing, methylated sites are identified as C reads.
Mass Spectrometry
Mass spectrometry can quantify modified nucleosides in tRNA. After enzymatic digestion of tRNA, nucleosides are analyzed by LC-MS/MS to detect and quantify m5C, m3C, and other modifications. This method provides stoichiometric information.
Ribosome Profiling (Ribo-seq)
Ribo-seq measures translation efficiency and ribosome occupancy at codon resolution. By comparing wild-type and knockout cells, researchers can assess how loss of tRNA methylation affects global translation and codon-specific pausing.
CRISPR-Based Knockout and Knock-in
CRISPR/Cas9 technology enables the generation of knockout, point-mutation, and knock-in cell lines to study the function of tRNA methyltransferases. These models are essential for dissecting the causal roles of specific modifications in cellular processes and disease.
How CRISPR Can Be Used to Study GO:0016427 tRNA (cytidine) methyltransferase activity
Knockout
CRISPR knockout of tRNA (cytidine) methyltransferase genes (e.g., NSUN2, METTL6, TRDMT1) allows researchers to study loss-of-function phenotypes, including changes in tRNA modification, translation, and cell viability. These models are valuable for identifying the specific roles of each enzyme.
Point Mutation
Introducing point mutations in the catalytic domain of these enzymes via CRISPR can dissect the importance of specific residues for methyltransferase activity. For example, mutating the catalytic cysteine of Dnmt2 abolishes its activity, providing insights into mechanism.
Knock-in
Knock-in of tagged versions (e.g., GFP, FLAG) of tRNA methyltransferases enables visualization and immunoprecipitation studies. This approach helps determine subcellular localization and identify interacting partners.
Overexpression
CRISPR activation (CRISPRa) or cDNA overexpression can be used to increase the levels of tRNA methyltransferases, allowing study of gain-of-function effects, such as enhanced translation or oncogenic transformation.
How EDITGENE Supports tRNA (cytidine) methyltransferase activity Research
Researchers studying tRNA (cytidine) methyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in a specific cellular process or disease. EDITGENE provides a comprehensive suite of CRISPR-based services to accelerate this research, from gene knockout to precise point mutations and knock-in models.
Contact EDITGENE today to design your custom CRISPR model for tRNA (cytidine) methyltransferase activity research.
Frequently Asked Questions About tRNA (cytidine) methyltransferase activity
What is tRNA (cytidine) methyltransferase activity?
It is the enzyme activity that adds a methyl group to cytidine residues in tRNA, using SAM as the methyl donor, as defined by GO:0016427.
What genes are involved in tRNA (cytidine) methyltransferase activity?
Key genes include TRDMT1 (Dnmt2), METTL6, NSUN2, NSUN6, and NSUN3, among others.
What diseases are associated with tRNA cytidine methylation?
Dysregulation is linked to cancer, neurological disorders like intellectual disability, and immune dysfunction such as IgA nephropathy.
How can I study tRNA (cytidine) methyltransferase activity?
Methods include RNA bisulfite sequencing, mass spectrometry, Ribo-seq, and CRISPR-based knockout or knock-in models.
What is the role of NSUN2 in tRNA methylation?
NSUN2 methylates cytosine at positions 34, 40, 48, and 49 in various tRNAs, affecting translation and cell proliferation.
What is the difference between m5C and m3C in tRNA?
m5C is 5-methylcytosine, while m3C is 3-methylcytosine; both are catalyzed by different enzymes and have distinct effects on tRNA structure and function.
Can CRISPR be used to study tRNA methyltransferases?
Yes, CRISPR knockout, point mutation, and knock-in models are powerful tools to dissect gene function and disease mechanisms.
What is the clinical relevance of METTL6?
METTL6 is overexpressed in hepatocellular carcinoma and promotes tumor growth, making it a potential therapeutic target.
How does Dnmt2 differ from other tRNA methyltransferases?
Dnmt2 (TRDMT1) primarily methylates C38 in tRNAAsp, tRNAGly, and tRNAVal, and is conserved from yeast to humans.
What services does EDITGENE offer for tRNA methylation research?
EDITGENE provides knockout, point mutation, knock-in, overexpression cell models, CRISPR library screening, and bioinformatics support.
Conclusion
tRNA (cytidine) methyltransferase activity (GO:0016427) is a fundamental molecular function that ensures proper tRNA modification and translation. Its dysregulation is implicated in cancer, neurological disorders, and immune diseases. Advances in CRISPR technology and sequencing methods continue to unravel the complex roles of these enzymes, offering new avenues for therapeutic intervention. EDITGENE is committed to supporting this research with state-of-the-art CRISPR services.
References
- 1. Zhang YY et al.. 2025. A cohort of mRNAs undergo high-stoichiometry NSUN6-mediated site-specific m(5)C modification.. Nat Commun 16(1):6119 PMID: 40615396
- 2. Yu S et al.. 2024. B-Cell Epigenetic Modulation of IgA Response by 5-Azacytidine and IgA Nephropathy.. J Am Soc Nephrol 35(12):1686-1701 PMID: 39137052
- 3. Canepa J et al.. 2026. Substrate selectivity of the human RNA m(5)C methyltransferase NSUN2.. Nature 655(8123):801-808 PMID: 42203868
- 4. Li S et al.. 2022. Structural basis for METTL6-mediated m3C RNA methylation.. Biochem Biophys Res Commun 589:159-164 PMID: 34922197
- 5. Kaiser S et al.. 2017. The RNA methyltransferase Dnmt2 methylates DNA in the structural context of a tRNA.. RNA Biol 14(9):1241-1251 PMID: 27819523
- 6. Arimbasseri AG et al.. 2016. Evolving specificity of tRNA 3-methyl-cytidine-32 (m3C32) modification: a subset of tRNAsSer requires N6-isopentenylation of A37.. RNA 22(9):1400-10 PMID: 27354703
- 7. Dai W et al.. 2023. Chemoproteomic Approaches to Studying RNA Modification-Associated Proteins.. Acc Chem Res 56(19):2726-2739 PMID: 37733063
- 8. Scheitl CPM et al.. 2022. Structure and mechanism of the methyltransferase ribozyme MTR1.. Nat Chem Biol 18(5):547-555 PMID: 35301481
