Methylation of 5'-5' confronting dinucleotides by vaccinia associated enzyme system

Methylation of a series of the 5'-5' confronting dinucleotides containing various number of phosphates was examined by the use of virion enzyme system of vaccinia virus. Methylation was absolutely dependent on the number of interposed phosphate groups between 5'-5' confronting dinucleotides, showing maximum efficiency in the 3 phosphate compound corresponding to the blocked 5'-terminus (cap) of an eukaryotic mRNA. Methylation, if any, occurred only at the 7-position of guanine residue, but not at the 2' position of ribose moiety.