Target Identification for the RsmG Methyltransferase at 16S rRNA Nucleotide G527 and Characterization of Bacillus subtilis rsmG Mutants

National Food Research Institute, Tsukuba, Ibaraki 305-8642, Department of Applied Biological Chemistry, Faculty of Agriculture, Shizuoka University, Shizuoka 422-8529, Japan, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark, and Laboratory of Molecular Genetics and Reserch Information Center for Extremophile, College of Science, Rikkyo University, Tokyo 171-8501, Japan

^* To whom correspondence should be addressed. Email: kochi{at}affrc.go.jp.

	Abstract

The methyltransfarase RsmG methylates the N7 position of nucleotide G535 in 16S rRNA of Bacillus subtilis (corresponding to G527 in Escherichia coli). Disruption of rsmG resulted in low-level resistance to streptomycin. Growth competition assay revealed that there are no differences in fitness between the rsmG mutant and parent strains under the various culture conditions examined. B. subtilis rsmG mutants emerged spontaneously at a relatively high frequency of 10^-6. Importantly, in the rsmG mutant background, high-level streptomycin-resistant rpsL (encoding ribosomal protein S12) mutants emerged at a frequency 200 times greater than that seen for the wild-type strain. This elevated frequency in the emergence of high-level streptomycin-resistance was facilitated by a more varied mutation pattern in rpsL than that obtained by selection of the wild-type strain.