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Gene Review

TGS1  -  Tgs1p

Saccharomyces cerevisiae S288c

Synonyms: Cap-specific guanine-N2 methyltransferase, P2573, Trimethylguanosine synthase, YPL157W, snRNA/snoRNA cap hypermethylase
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High impact information on TGS1

  • In yeast, U3 follows a similar maturation pathway, and equivalent 3'-extended precursors are enriched in the nucleolus and in the nucleolar body, a nucleolar domain that concentrates Tgs1p under certain growth conditions [1].
  • Here we report that the Saccharomyces cerevisiae nucleolar trimethyl guanosine synthase I (Tgs1p), which specifically selects the m(7)G cap structure of snRNAs and snoRNAs for m(2,2,7)G conversion, is required not only for efficient pre-mRNA splicing but also for pre-rRNA processing and small ribosomal subunit synthesis [2].
  • Mutational analysis indicates that the requirement for Tgs1p in pre-mRNA splicing, but not its involvement in ribosome synthesis, is dependent upon its function in cap trimethylation [2].
  • The m(2,7)GDP product formed by Tgs2 can be converted to m(2,2,7)GDP by S. pombe Tgs1 in the presence of excess AdoMet [3].
  • Tgs1 is the enzyme responsible for converting 7-methylguanosine RNA caps to the 2,2,7-trimethylguanosine cap structures of small nuclear and small nucleolar RNAs [3].

Biological context of TGS1

  • We conclude that Tgs1 is guanine-specific, that N7 methylation must precede N2 methylation, that Tgs1 acts via a distributive mechanism, and that the chemical steps of TMG synthesis do not require input from RNA or protein cofactors [4].
  • Inhibition of PIMT/Tgs1 expression by siRNA in HeLa cells resulted in an increase in the percentage of cells in G2/M phases [5].
  • To further characterize functional domains of Tgs1, mutants were constructed and tested for their effects on cell viability, subcellular localization and binding to the small nuclear ribonucleoproteins (snRNPs) and small nucleolar RNPs (snoRNPs) [6].

Anatomical context of TGS1

  • Here, we show that trimethylguanosine synthase 1 (TGS1), the human homologue of the yeast snRNA cap hypermethylase, interacts directly with the survival of motor neuron (SMN) protein [7].

Associations of TGS1 with chemical compounds

  • Tgs1 also methylates the cap analog m(7)GpppA but is unreactive with GTP, GDP, GpppA, m2,2,7GTP, m2,2,7GDP, ATP, CTP, UTP, and ITP [4].

Analytical, diagnostic and therapeutic context of TGS1

  • Site- directed mutagenesis of Tgs1 allowed also the identification of the residues likely to be involved in the formation of the m7G-binding site and the catalytic center [6].


  1. Mammalian and yeast U3 snoRNPs are matured in specific and related nuclear compartments. Verheggen, C., Lafontaine, D.L., Samarsky, D., Mouaikel, J., Blanchard, J.M., Bordonné, R., Bertrand, E. EMBO J. (2002) [Pubmed]
  2. The small nucle(ol)ar RNA cap trimethyltransferase is required for ribosome synthesis and intact nucleolar morphology. Colau, G., Thiry, M., Leduc, V., Bordonné, R., Lafontaine, D.L. Mol. Cell. Biol. (2004) [Pubmed]
  3. Giardia lamblia RNA cap guanine-N2 methyltransferase (Tgs2). Hausmann, S., Shuman, S. J. Biol. Chem. (2005) [Pubmed]
  4. Specificity and mechanism of RNA cap guanine-N2 methyltransferase (Tgs1). Hausmann, S., Shuman, S. J. Biol. Chem. (2005) [Pubmed]
  5. Different isoforms of PRIP-interacting protein with methyltransferase domain/trimethylguanosine synthase localizes to the cytoplasm and nucleus. Enünlü, I., Pápai, G., Cserpán, I., Udvardy, A., Jeang, K.T., Boros, I. Biochem. Biophys. Res. Commun. (2003) [Pubmed]
  6. Sequence-structure-function relationships of Tgs1, the yeast snRNA/snoRNA cap hypermethylase. Mouaikel, J., Bujnicki, J.M., Tazi, J., Bordonné, R. Nucleic Acids Res. (2003) [Pubmed]
  7. Interaction between the small-nuclear-RNA cap hypermethylase and the spinal muscular atrophy protein, survival of motor neuron. Mouaikel, J., Narayanan, U., Verheggen, C., Matera, A.G., Bertrand, E., Tazi, J., Bordonné, R. EMBO Rep. (2003) [Pubmed]
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