RNA cap guanine-N2 methyltransferases such as Schizosaccharomyces pombe Tgs1 and Giardia lamblia Tgs2 catalyse methylation of the exocyclic N2 amine of 7-methylguanosine .
RNA cap guanine-N2 methyltransferases such as Schizosaccharomyces pombe (Fission yeast) trimethylguanosine synthase (Tgs1) and Giardia lamblia (Giardia intestinalis) Tgs2, catalyse the methylation step(s) for the conversion of the 7-monomethylguanosine (m(7)G) caps of snRNAs and snoRNAs to a 2,2,7-trimethylguanosine (m(2,2,7)G) cap structure [PUBMED:17284461, PUBMED:18840651, PUBMED:15590684]. Trimethylguanosine synthase is specific for guanine, and N7 methylation must precede N2 methylation. This enzyme is required for pre-mRNA splicing, pre-rRNA processing and small ribosomal subunit synthesis. As such, this enzyme plays a role in transcriptional regulation.