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Journal of Bacteriology, May 2004, p. 2735-2744, Vol. 186, No. 9
0021-9193/04/$08.00+0 DOI: 10.1128/JB.186.9.2735-2744.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Department of Genetics, Institute of Molecular and Cell Biology, Tartu University and Estonian Biocentre, 51010 Tartu, Estonia
Received 8 December 2003/ Accepted 23 January 2004
In this work we studied involvement of DNA polymerase IV (Pol IV) (encoded by the dinB gene) in stationary-phase mutagenesis in Pseudomonas putida. For this purpose we constructed a novel set of assay systems that allowed detection of different types of mutations (e.g., 1-bp deletions and different base substitutions) separately. A significant effect of Pol IV became apparent when the frequency of accumulation of 1-bp deletion mutations was compared in the P. putida wild-type strain and its Pol IV-defective dinB knockout derivative. Pol IV-dependent mutagenesis caused a remarkable increase (approximately 10-fold) in the frequency of accumulation of 1-bp deletion mutations on selective plates in wild-type P. putida populations starved for more than 1 week. No effect of Pol IV on the frequency of accumulation of base substitution mutations in starving P. putida cells was observed. The occurrence of 1-bp deletions in P. putida cells did not require a functional RecA protein. RecA independence of Pol IV-associated mutagenesis was also supported by data showing that transcription from the promoter of the P. putida dinB gene was not significantly influenced by the DNA damage-inducing agent mitomycin C. Therefore, we hypothesize that mechanisms different from the classical RecA-dependent SOS response could elevate Pol IV-dependent mutagenesis in starving P. putida cells.
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