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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
Author(s) -
Steven Slater,
M. R. Lifsics,
Michael O’Donnell,
Russell Maurer
Publication year - 1994
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.176.3.815-821.1994
Subject(s) - biology , mutant , dna polymerase , suppressor mutation , microbiology and biotechnology , polymerase , protein subunit , genetics , gene
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.

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