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Effect of deletion of SOS‐induced polymerases, pol II, IV, and V, on spontaneous mutagenesis in Escherichia coli mutD5
Author(s) -
Nowosielska Anetta,
Janion Celina,
Grzesiuk Elzbieta
Publication year - 2004
Publication title -
environmental and molecular mutagenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1
H-Index - 87
eISSN - 1098-2280
pISSN - 0893-6692
DOI - 10.1002/em.20019
Subject(s) - dna polymerase , proofreading , processivity , mutagenesis , biology , microbiology and biotechnology , rna polymerase iii , polymerase , mutation , mutant , escherichia coli , mutation frequency , genetics , reversion , dna , gene , rna polymerase , phenotype
The E. coli dna Q gene encodes the ϵ subunit of DNA polymerase III (pol III) responsible for the proofreading activity of this polymerase. The mutD5 mutant of dna Q chronically expresses the SOS response and exhibits a mutator phenotype. In this study we have constructed a set of E. coli AB1157 mutD5 derivatives deleted in genes encoding SOS‐induced DNA polymerases, pol II, pol IV, and pol V, and estimated the frequency and specificity of spontaneous argE3 →Arg + reversion in exponentially growing and stationary‐phase cells of these strains. We found that pol II exerts a profound effect on the specificity of spontaneous mutation in exponentially growing cells. Analysis of growth‐dependent Arg + revertants in mutD5 polB + strains revealed that Arg + revertants were due to tRNA suppressor formation, whereas those in mutD5 Δ polB strains arose by back mutation at the argE3 ochre site. In stationary‐phase bacteria, Arg + revertants arose mainly by back mutation, regardless of whether they were proficient or deficient in pol II. Our results also indicate that in a mutD5 background, the absence of pol II led to increased frequency of Arg + growth‐dependent revertants, whereas the lack of pol V caused its dramatic decrease, especially in mutD5 Δ umuDC and mutD5 Δ umuDC Δ polB strains. In contrast, the rate of stationary‐phase Arg + revertants increased in the absence of pol IV in the mutD5 Δ dinB strain. We postulate that the proofreading activity of pol II excises DNA lesions in exponentially growing cells, whereas pol V and pol IV are more active in stationary‐phase cultures. Environ. Mol. Mutagen. 43:226–234, 2004. © 2004 Wiley‐Liss, Inc.