Identification of the 16S rRNA m(5)C967 methyltransferase from Escherichiacoli

The fmu gene product has been proposed to be an RNA methyltransferase [Koon in, E. V. (1994) Nucleic Acids Res. 22, 2476-2478], Fmu has been cloned and expressed, and the encoded 47 kDa protein has been purified and characteri zed. The enzyme catalyzed specific methylation of C967 of unmodified 16S rR NA transcripts. A 16mer stem-loop structure containing C967 (nt 960-975) wa s also a good substrate for the enzyme in vitro. Methylation of C967 was co nfirmed by several methods including analysis of RNase TI digests and neare st-neighbor analysis. Fmu did not catalyze methylation of transcripts of 23 S rRNA, E, coli cells that contained kan(r)-disrupted fmu produced 16S rRNA that could be specifically methylated by Fmu in vitro at C967 but not C140 7. Further, fmu disruption did not significantly alter the growth rate of E , coli in rich or minimal media. We propose renaming this ORF "rrmB" and th e enzyme "RrmB" for rRNA methyltransferase.