Phylogenetic analysis of the eukaryotic RNA (cytosine-5)-methyltransferases.

RNA (cytosine-5)-methyltransferases (RCMTs) have been characterized both in prokaryotic and eukaryotic organisms. The RCMT family, however, remains largely uncharacterized, as opposed to the family of DNA (cytosine-5)-methyltransferases which has been studied in depth. In the present study, an in silico identification of the putative 5-methylcytosine RNA-generating enzymes in the eukaryotic genomes was performed. A comprehensive phylogenetic analysis of the putative eukaryotic RCMT-related proteins has been performed in order to redefine subfamilies within the RCMT family. Five distinct eukaryotic subfamilies were identified, including the three already known (NOP2, NCL1 and YNL022c), one novel subfamily (RCMT9) and a fifth one which hitherto was considered to exist exclusively in prokaryotes (Fmu). The potential evolutionary relationships among the different eukaryotic RCMT subfamilies were also investigated. Furthermore, the results of this study add further support to a previous hypothesis that RCMTs represent evolutionary intermediates of RNA (uridine-5)-methyltransferases and DNA (cytosine-5)-methyltransferases.