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Journal of Bacteriology, December 2006, p. 8573-8585, Vol. 188, No. 24
0021-9193/06/$08.00+0     doi:10.1128/JB.01481-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Role of Pseudomonas aeruginosa dinB-Encoded DNA Polymerase IV in Mutagenesis

Laurie H. Sanders,^1, Andrea Rockel,^2, Haiping Lu,² Daniel J. Wozniak,² and Mark D. Sutton^1*

Department of Biochemistry, School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, 3435 Main Street, 140 Farber Hall, Buffalo, New York 14214,¹ Department of Microbiology and Immunology, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157²

Received 19 September 2006/ Accepted 5 October 2006

Pseudomonas aeruginosa is a human opportunistic pathogen that chronically infects the lungs of cystic fibrosis patients and is the leading cause of morbidity and mortality of people afflicted with this disease. A striking correlation between mutagenesis and the persistence of P. aeruginosa has been reported. In other well-studied organisms, error-prone replication by Y family DNA polymerases contributes significantly to mutagenesis. Based on an analysis of the PAO1 genome sequence, P. aeruginosa contains a single Y family DNA polymerase encoded by the dinB gene. As part of an effort to understand the mechanisms of mutagenesis in P. aeruginosa, we have cloned the dinB gene of P. aeruginosa and utilized a combination of genetic and biochemical approaches to characterize the activity and regulation of the P. aeruginosa DinB protein (DinB_Pa). Our results indicate that DinB_Pa is a distributive DNA polymerase that lacks intrinsic proofreading activity in vitro. Modest overexpression of DinB_Pa from a plasmid conferred a mutator phenotype in both Escherichia coli and P. aeruginosa. An examination of this mutator phenotype indicated that DinB_Pa has a propensity to promote CA transversions and –1 frameshift mutations within poly(dGMP) and poly(dAMP) runs. The characterization of lexA⁺ and lexA::aacC1 P. aeruginosa strains, together with in vitro DNA binding assays utilizing cell extracts or purified P. aeruginosa LexA protein (LexA_Pa), indicated that the transcription of the dinB gene is regulated as part of an SOS-like response. The deletion of the dinB_Pa gene sensitized P. aeruginosa to nitrofurazone and 4-nitroquinoline-1-oxide, consistent with a role for DinB_Pa in translesion DNA synthesis over N²-dG adducts. Finally, P. aeruginosa exhibited a UV-inducible mutator phenotype that was independent of dinB_Pa function and instead required polA and polC, which encode DNA polymerase I and the second DNA polymerase III enzyme, respectively. Possible roles of the P. aeruginosa dinB, polA, and polC gene products in mutagenesis are discussed.

Published ahead of print on 13 October 2006.

These authors contributed equally.

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