Catalysis of two successive methyl transfer reactions from AdoMet to the N-2 atom of guanosine, thereby converting 7-methylguanosine in an RNA cap to 2,2,7 trimethylguanosine.
Comment:
A 2,2,7-trimethylguanosine (TMG) cap is found on many RNA polymerase II transcribed small noncoding RNAs including small nuclear RNA (snRNA), small nucleolar RNA (snoRNA) and telomerase RNA. It is also found on nematode mRNAs that undergo trans-splicing of a 5'-capped leader sequence.
Synonyms:
exact_synonym:
RNA trimethylguanosine synthase activity; cap hypermethylase activity
related_synonym:
small nuclear RNA methyltransferase activity; snRNA methyltransferase activity