Site-specific RNA methylation by a methyltransferase ribozyme

Nearly all classes of coding and non-coding RNA undergo post-transcriptional modification including RNA methylation. Methylated nucleotides belong to the evolutionarily most conserved features of tRNA and rRNA.(1,2) Many contemporary methyltransferases use the universal cofactor S-adenosylmethionine (SAM) as methyl group donor. This and other nucleotide-derived cofactors are considered as evolutionary leftovers from an RNA World, in which ribozymes may have catalysed essential metabolic reactions beyond self-replication.(3) Chemically diverse ribozymes seem to have been lost in Nature, but may be reconstructed in the laboratory by in vitro selection. Here, we report a methyltransferase ribozyme that catalyses the site-specific installation of 1-methyladenosine (m(1)A) in a substrate RNA, utilizing O(6)-methylguanine (m(6)G) as a small-molecule cofactor. The ribozyme shows a broad RNA sequence scope, as exemplified by site-specific adenosine methylation in tRNAs. This finding provides fundamental insights into RNA’s catalytic abilities, serves a synthetic tool to install m(1)A in RNA, and may pave the way to in vitro evolution of other methyltransferase and demethylase ribozymes.