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Journal of Bacteriology, October 2007, p. 6976-6988, Vol. 189, No. 19
0021-9193/07/$08.00+0     doi:10.1128/JB.00776-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The mutT Defect Does Not Elevate Chromosomal Fragmentation in Escherichia coli Because of the Surprisingly Low Levels of MutM/MutY-Recognized DNA Modifications{triangledown}

Ella Rotman and Andrei Kuzminov*

Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois

Received 18 May 2007/ Accepted 28 June 2007

Nucleotide pool sanitizing enzymes Dut (dUTPase), RdgB (dITPase), and MutT (8-oxo-dGTPase) of Escherichia coli hydrolyze noncanonical DNA precursors to prevent incorporation of base analogs into DNA. Previous studies reported dramatic AT->CG mutagenesis in mutT mutants, suggesting a considerable density of 8-oxo-G in DNA that should cause frequent excision and chromosomal fragmentation, irreparable in the absence of RecBCD-catalyzed repair and similar to the lethality of dut recBC and rdgB recBC double mutants. In contrast, we found mutT recBC double mutants viable with no signs of chromosomal fragmentation. Overproduction of the MutM and MutY DNA glycosylases, both acting on DNA containing 8-oxo-G, still yields no lethality in mutT recBC double mutants. Plasmid DNA, extracted from mutT mutM double mutant cells and treated with MutM in vitro, shows no increased relaxation, indicating no additional 8-oxo-G modifications. Our {Delta}mutT allele elevates the AT->CG transversion rate 27,000-fold, consistent with published reports. However, the rate of AT->CG transversions in our mutT+ progenitor strain is some two orders of magnitude lower than in previous studies, which lowers the absolute rate of mutagenesis in {Delta}mutT derivatives, translating into less than four 8-oxo-G modifications per genome equivalent, which is too low to cause the expected effects. Introduction of various additional mutations in the {Delta}mutT strain or treatment with oxidative agents failed to increase the mutagenesis even twofold. We conclude that, in contrast to the previous studies, there is not enough 8-oxo-G in the DNA of mutT mutants to cause elevated excision repair that would trigger chromosomal fragmentation.

* Corresponding author. Mailing address: Department of Microbiology, University of Illinois at Urbana-Champaign, B103 C&LSL, 601 South Goodwin Ave., Urbana IL 61801-3709. Phone: (217) 265-0329. Fax: (217) 244-6697. E-mail: kuzminov{at}life.uiuc.edu

{triangledown} Published ahead of print on 6 July 2007.

Journal of Bacteriology, October 2007, p. 6976-6988, Vol. 189, No. 19
0021-9193/07/$08.00+0     doi:10.1128/JB.00776-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Amado, L., Kuzminov, A. (2009). Polyphosphate Accumulation in Escherichia coli in Response to Defects in DNA Metabolism. J. Bacteriol. 191: 7410-7416 [Abstract] [Full Text]  


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