This Article Full Text Full Text (PDF) Supplemental material Other Versions of this Article: JB.00173-08v1 190/15/5239    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Google Scholar Articles by Pohlhaus, J. R. Articles by Kreuzer, K. N. PubMed PubMed Citation Articles by Pohlhaus, J. R. Articles by Kreuzer, K. N.

 Previous Article  |  Next Article 

Journal of Bacteriology, August 2008, p. 5239-5247, Vol. 190, No. 15
0021-9193/08/$08.00+0     doi:10.1128/JB.00173-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Subunit of DNA Polymerase III Is Involved in the Nalidixic Acid-Induced SOS Response in Escherichia coli ^,

Jennifer Reineke Pohlhaus, David T. Long, Erin O'Reilly, and Kenneth N. Kreuzer^*

Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710

Received 4 February 2008/ Accepted 19 May 2008

Quinolone antibacterial drugs such as nalidixic acid target DNA gyrase in Escherichia coli. These inhibitors bind to and stabilize a normally transient covalent protein-DNA intermediate in the gyrase reaction cycle, referred to as the cleavage complex. Stabilization of the cleavage complex is necessary but not sufficient for cell killing—cytotoxicity apparently results from the conversion of cleavage complexes into overt DNA breaks by an as-yet-unknown mechanism(s). Quinolone treatment induces the bacterial SOS response in a RecBC-dependent manner, arguing that cleavage complexes are somehow converted into double-stranded breaks. However, the only proteins known to be required for SOS induction by nalidixic acid are RecA and RecBC. In hopes of identifying additional proteins involved in the cytotoxic response to nalidixic acid, we screened for E. coli mutants specifically deficient in SOS induction upon nalidixic acid treatment by using a dinD::lacZ reporter construct. From a collection of SOS partially constitutive mutants with disruptions of 47 different genes, we found that dnaQ insertion mutants are specifically deficient in the SOS response to nalidixic acid. dnaQ encodes DNA polymerase III subunit, the proofreading subunit of the replicative polymerase. The deficient response to nalidixic acid was rescued by the presence of the wild-type dnaQ gene, confirming involvement of the subunit. To further characterize the SOS deficiency of dnaQ mutants, we analyzed the expression of several additional SOS genes in response to nalidixic acid using real-time PCR. A subset of SOS genes lost their response to nalidixic acid in the dnaQ mutant strain, while two tested SOS genes (recA and recN) continued to exhibit induction. These results argue that the replication complex plays a role in modulating the SOS response to nalidixic acid and that the response is more complex than a simple on/off switch.

Published ahead of print on 6 June 2008.

Supplemental material for this article may be found at http://jb.asm.org/.

Present address: Department of Medicine, Division of Oncology, Duke University Medical Center, Durham, NC 27705.