holE, the gene coding for the theta subunit of DNA polymerase III of Escherichia coli: characterization of a holE mutant and comparison with a dnaQ (epsilon-subunit) mutant.
DNA polymerase III holoenzyme is a multiprotein complex responsible for the bulk of chromosomal replication in Escherichia coli and Salmonella typhimurium. The catalytic core of the holoenzyme is an alpha epsilon theta heterotrimer that incorporates both a polymerase subunit (alpha; dnaE) and a proofreading subunit (epsilon; dnaQ). The role of theta is unknown. Here, we describe a null mutation of holE, the gene for theta. A strain carrying this mutation was fully viable and displayed no mutant phenotype. In contrast, a dnaQ null mutant exhibited poor growth, chronic SOS induction, and an elevated spontaneous mutation rate, like dnaQ null mutants of S. typhimurium described previously. The poor growth was suppressible by a mutation affecting alpha which was identical to a suppressor mutation identified in S. typhimurium. A double mutant null for both holE and dnaQ was indistinguishable from the dnaQ single mutant. These results show that the theta subunit is dispensable in both dnaQ+ and mutant dnaQ backgrounds, and that the phenotype of epsilon mutants cannot be explained on the basis of interference with theta function.
Slater
S C
SC
Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4960.
Lifsics
M R
MR
O'Donnell
M
M
Maurer
R
R
D004258:DNA Polymerase III / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005798:Genes, Bacterial; D016153:Genes, Suppressor; D016254:Mutagenesis, Insertional; D013014:SOS Response, Genetics; D013329:Structure-Activity Relationship
C074904:DNA polymerase III, alpha subunit; D004258:DNA Polymerase III