Existence of methylated messenger RNA in mouse L cells

Messenger RNA of mouse L cells is methylated in both base and ribose moieties. On the average there are about 2.2 methyl groups per 1000 nucleotides in mRNA, a proportion which is about one-sixth that of mammalian ribosomal RNA. The variety of methylated bases in mRNA is more limited than in ribosomal RNA. A very low level of methylation is detected in heterogeneous nuclear RNA, suggesting that methylation, like polyadenylation, may constitute a post-transcriptional modification of messenger RNA precursor in eucaryotic cells.