Translational defects of Escherichia coli mutants deficient in the Um(2552) 23S ribosomal RNA methyltransferase RrmJ/FTSJ

We recently identified RrmJ (alias FtsJ), the first encoded protein of the rrmJ-hflB heat shock operon, as an Um(2552) methyltransferase of the 23S rR NA. We now report that the rrmJ-deficient strain exhibits growth and transl ational defects compared to the wild-type strain. Growth rates of the rrmJ mutant are decreased at both low and high temperatures. Protein synthesis a ctivity is reduced up to 65% when S-30 rrmJ mutant extracts are tested in a coupled in vitro transcription/translation assay. In vitro methylation of these extracts by RrmJ partially restores protein synthesis activity. Polys ome profile analysis of the rrmJ strain reveals an increase in the proporti on of free 30S and 50S subunits at both 30 and 42 degrees C. These results suggest that the RrmJ-catalyzed methylation of Um(2552) in 23S RNA strength ens ribosomal subunit interactions, increases protein synthesis activity, a nd improves cell growth rates even at non-heat shock. temperatures. (C) 200 0 Academic Press.