Specificity of Escherichia coli mutD and mutL mutator strains

UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology



Document Type


Medical Subject Headings

Coliphages; DNA Polymerase III; DNA Repair; Escherichia coli; Escherichia coli Proteins; *Genes, Bacterial; *Genes, Viral; Methyltransferases; *Mutation; Plasmids; Promoter Regions, Genetic; *Site-Specific DNA-Methyltransferase (Adenine-Specific)


The products of the mutD and mutL genes of Escherichia coli are involved in proofreading by DNA polymerase III and DNA adenine MTase (Dam)-dependent mismatch repair, respectively. We have used the plasmid-borne bacteriophage P22 mnt gene as a target to determine the types of mutations produced in mutL25 and mutD5 strains. Of 60 mutations identified from mutL25 cells, 52 were transition mutations and of these the AT----GC subset predominated (40 out of 52). The majority of AT----GC mutations were found at the same three sites (hotspots). In contrast, transversion mutations (47 out of 76) were found about twice as frequently as transitions (28 out of 76) from mutD5 bacteria. Two hotspots were identified but at different sites than those in the mutL25 cells. These results suggest that the proofreading function of DNA polymerase III primarily repairs potential transversion mutations while Dam-dependent mismatch repair rectifies potential transition mutations.

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Citation: Gene. 1990 Mar 1;87(1):1-5.

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