| Type: | Family | Name: | RNA (C5-cytosine) methyltransferase |
| Description: | RNA (C5-cytosine) methyltransferases (RCMTs) catalyse the transfer of a methyl group to the 5th carbon of a cytosine base in RNA sequences to produce C5-methylcytosine. RCMTs use the cofactor S-adenosyl-L-methionine (SAM) as a methyl donor []. The catalytic mechanism of RCMTs involves an attack by the thiolate of a Cys residue on position 6 of the target cytosine base to form a covalent link, thereby activating C5 for methyl-group transfer. Following the addition of the methyl group, a second Cys residue acts as a general base in the beta-elimination of the proton from the methylated cytosine ring. The free enzyme is restored and the methylated product is released [].Numerous putative RCMTs have been identified in archaea, bacteria and eukaryota [, ]; most are predicted to be nuclear or nucleolar proteins []. The Escherichia coli Ribosomal RNA Small-subunit Methyltransferase Beta (RSMB) FMU (FirMicUtes) represents the first protein identified and characterised as a cytosine-specific RNA methyltransferase. RSMB was reported to catalyse the formation of C5-methylcytosine at position 967 of 16S rRNA [, ].A classification of RCMTs has been proposed on the basis of sequence similarity []. According to this classification, RCMTs are divided into 8 distinct subfamilies []. Recently, a new RCMT subfamily, termed RCMT9, was identified []. Members of the RCMT contain a core domain, responsible for the cytosine-specific RNA methyltransferase activity. This 'catalytic' domain adopts the Rossmann fold for the accommodation of the cofactor SAM []. The RCMT subfamilies are also distinguished by N-terminal and C-terminal extensions, variable both in size and sequence []. | Short Name: | RCMT |
| DB identifier | Type | Name |
|---|---|---|
| IPR023269 | Family | RNA (C5-cytosine) methyltransferase, subfamily 9 |
| IPR023273 | Family | RNA (C5-cytosine) methyltransferase, NOP2 |
| IPR004573 | Family | rRNA small subunit methyltransferase B |
| IPR023268 | Family | RNA (C5-cytosine) methyltransferase, putative Rsm-related, plant |
| IPR023270 | Family | tRNA (C5-cytosine) methyltransferase, NCL1 |
| IPR023545 | Family | rRNA small subunit methyltransferase F |
