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

Abstract

ABSTRACT 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 C→A transversions and −1 frameshift mutations within poly(dGMP) and poly(dAMP) runs. The characterization of lexA + and Δ 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 N 2 -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.