The FtsJ/RrmJ heat shock protein of Escherichia coli is a 23 S ribosomal RNA methyltransferase

Ribosomal RNAs undergo several nucleotide modifications including methylati on. We identify FtsJ, the first encoded protein of the ftsJ-hflB heat shock operon, as an Escherichia coli methyltransferase of the 23 S rRNA. The met hylation reaction requires S-adenosylmethionine as donor of methyl groups, purified FtsJ or a S-150 supernatant from an FtsJ-producing strain, and rib osomes from an FtsJ-deficient strain. In vitro, FtsJ does not efficiently m ethylate ribosomes purified from a strain producing FtsJ, suggesting that t hese ribosomes are already methylated in vivo by FtsJ. FtsJ is active on ri bosomes and on the 50 S ribosomal subunit, but is inactive on free rRNA sug gesting that its natural substrate is ribosomes or a pre-ribosomal ribonucl eoprotein particle. We identified the methylated nucleotide as 2'-O-methylu ridine 2552, by reverse phase high performance liquid chromatography analys is, boronate affinity chromatography, and hybridization-protection experime nts. In view of its newly established function, FtsJ is renamed RrmJ and it s encoding gene, rrmJ.