Exposition of a family of RNA m(5)C methyltransferases from searching genomic and proteomic sequences

The Escherichia coli fmu gene product has recently been determined to be th e 16S rRNA m(5)C 967 methyltransferase, As such, Fmu represents the first p rotein identified as an S-adenosyl-L-methionine (AdoMet)-dependent RNA m(5) C methyltransferase whose amino acid sequence is known. Using the amino aci d sequence of Fmu as an initial probe in an iterative search of completed D NA sequence databases, 27 homologous ORF products were identified as probab le RNA m(5)C methyltransferases. Further analysis of sequences in undeposit ed genomic sequencing data and EST databases yielded more than 30 additiona l homologs. These putative RNA m(5)C methyltransferases are grouped into ei ght subfamilies, some of which are predicted to consist of direct genetic c ounterparts, or orthologs, The enzymes proposed to be RNA m(5)C methyltrans ferases have sequence motifs closely related to signature sequences found i n the well-studied DNA m(5)C methyltransferases and other AdoMet-dependent methyltransferases, Structure-function correlates in the known AdoMet methy ltransferases support the assignment of this family as RNA m(5)C methyltran sferases.