This Article Full Text (PDF) 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 Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rossi, S C Articles by Topal, M D Search for Related Content PubMed PubMed Citation Articles by Rossi, S C Articles by Topal, M D

 Previous Article  |  Next Article 

J Bacteriol. 1991 February; 173(3): 1201-1207

research-article

Mutagenic frequencies of site-specifically located O6-methylguanine in wild-type Escherichia coli and in a strain deficient in ada-methyltransferase.

S C Rossi and M D Topal

Department of Pathology, University of North Carolina Medical School, Chapel Hill 27599-7295.

ABSTRACT

The adaptive response of Escherichia coli involves protection of the cells against the toxic and mutagenic consequences of exposure to high doses of a methylating agent by prior exposure to low doses of the agent. Ada protein, a major repair activity for O6-methylguanine, is activated to positively control the adaptive response; O6-methylguanine is one of the major mutagenic lesions produced by methylating agents. We investigated the mutation frequency of wild-type Escherichia coli and strains containing the ada-5 mutation in response to site-specifically synthesized O6-methylguanine under conditions in which the adaptive response was not induced. Site-directed mutagenesis and oligonucleotide self-selection techniques were used to isolate the progeny of M13mp18 DNAs constructed to contain O6-methylguanine at any of eight different positions. The progeny were isolated from E. coli strains isogeneic except for deficiency in Ada-methyltransferase repair, UvrABC excision repair, or both. The resulting O6-methylguanine mutation levels at each position were determined by using differential oligonucleotide hybridization. We found that the wild type had up to a 2.6-fold higher mutation frequency than ada-5 mutants. In addition, the mutation frequency varied with the position of the O6-methylguanine in the DNA in the wild type but not in ada-5 mutants; O6-methylguanine lesions at the 5' ends of runs of consecutive guanines gave the highest mutation frequencies. Determination of the mutation frequency of O6-methylguanine in wild-type and mutS cells showed that mismatch repair can affect O6-methylguanine mutation levels.

---

J Bacteriol. 1991 February; 173(3): 1201-1207

This article has been cited by other articles:

• Barvaux, V. A., Ranson, M., Brown, R., McElhinney, R. S., McMurry, T. B. H., Margison, G. P. (2004). Dual repair modulation reverses Temozolomide resistance in vitro. Molecular Cancer Therapeutics 3: 123-127 [Abstract] [Full Text]  
• Gerson, S. L. (2002). Clinical Relevance of MGMT in the Treatment of Cancer. JCO 20: 2388-2399 [Abstract] [Full Text]