Role of the RuvAB protein in avoiding spontaneous formation of deletion mutations in the Escherichia coli K-12 endogenous tonB gene |
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Authors: | Mashimo Kazumi Nagata Yuki Kawata Masakado Iwasaki Hiroshi Yamamoto Kazuo |
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Affiliation: | Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan. |
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Abstract: | The endogenous tonB gene of Escherichia coli was used as a target for spontaneous deletion mutations which were isolated from ruvAB-, recG-, and ruvC- cells. The rates of tonB mutation were essentially the same in ruv+, ruvAB-, recG-, and ruvC- cells. We analyzed tonB mutants by sequencing. In the ruv+, recG-, and ruvC- strains, the spectra were different from those obtained from the ruvAB- cells, where deletions dominated followed by IS insertions, base substitutions, and frameshifts, in that order. We then analyzed the tonB-trp large deletion, due to simultaneous mutations of the trp operon, and found that the frequency in ruvAB- was higher than those in ruv+, recG-, and ruvC- cells. To characterize deletion formation further, we analyzed all the tonB mutants from one colicin plate. Seven deletions were identified at five sites from the 45 tonB mutants of ruv+ cells and 24 deletions at 11 sites from the 43 tonB mutants of ruvAB- cells. Thus, the ruvAB- strain is a deletion mutator. We discuss the role of RuvAB in avoiding deletions. |
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Keywords: | Spontaneous mutagenesis tonB gene Deletion ruvAB recG ruvC Replication fork collapse |
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