Abstract
The mismatch repair system of Escherichia coli K12 removes mispaired bases from DNA. Mismatch repair can occur on either strand of DNA if it lacks N6-methyladenines within 5'-GATC-3' sequences. In hemimethylated heteroduplexes, repair occurs preferentially on the unmethylated strand. If both strands are fully methylated, repair is inhibited. Mutant (dam-) strains of E. coli defective in the adenine methylase that recognizes 5'-GATC-3' sequences (Dam), and therefore defective in mismatch repair, show increased spontaneous mutation rates compared to otherwise isogenic dam+ hosts. We have isolated and characterized 91 independent mutations that arise as a consequence of the Dam- defect in a plasmid-borne phage P22 repressor gene, mnt. The majority of these mutations are A:T→G:C transitions that occur within six base pairs of the two 5'-GATC-3' sequences in the mnt gene. In contrast, the spectrum of mnt- mutations in a dam+ host is comprised of a majority of insertions of IS elements and deletions that do not cluster near Dam recognition sites. These results show that Dam-directed post-replicative mismatch repair plays a significant role in the rectification of potential transition mutations in vivo, and suggest that sequences associated with Dam recognition sites are particularly prone to replication or repair errors.
Full Text
The Full Text of this article is available as a PDF (515.8 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Beckingham K., White R. The ribosomal DNA of Calliphora erythrocephala; and analysis of hybrid plasmids containing ribosomal DNA. J Mol Biol. 1980 Mar 15;137(4):349–373. doi: 10.1016/0022-2836(80)90162-x. [DOI] [PubMed] [Google Scholar]
- Loechler E. L., Green C. L., Essigmann J. M. In vivo mutagenesis by O6-methylguanine built into a unique site in a viral genome. Proc Natl Acad Sci U S A. 1984 Oct;81(20):6271–6275. doi: 10.1073/pnas.81.20.6271. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lu A. L., Clark S., Modrich P. Methyl-directed repair of DNA base-pair mismatches in vitro. Proc Natl Acad Sci U S A. 1983 Aug;80(15):4639–4643. doi: 10.1073/pnas.80.15.4639. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Miyake Y., Gaylor J. L., Morris H. P. Abnormal microsomal cytochromes and electron transport in Morris hepatomas. J Biol Chem. 1974 Mar 25;249(6):1980–1987. [PubMed] [Google Scholar]
- Ohtsubo H., Ohtsubo E. Nucleotide sequence of an insertion element, IS1. Proc Natl Acad Sci U S A. 1978 Feb;75(2):615–619. doi: 10.1073/pnas.75.2.615. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sanger F., Nicklen S., Coulson A. R. DNA sequencing with chain-terminating inhibitors. Proc Natl Acad Sci U S A. 1977 Dec;74(12):5463–5467. doi: 10.1073/pnas.74.12.5463. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sauer R. T., Krovatin W., DeAnda J., Youderian P., Susskind M. M. Primary structure of the immI immunity region of bacteriophage P22. J Mol Biol. 1983 Aug 25;168(4):699–713. doi: 10.1016/s0022-2836(83)80070-9. [DOI] [PubMed] [Google Scholar]
- Youderian P., Vershon A., Bouvier S., Sauer R. T., Susskind M. M. Changing the DNA-binding specificity of a repressor. Cell. 1983 Dec;35(3 Pt 2):777–783. doi: 10.1016/0092-8674(83)90110-1. [DOI] [PubMed] [Google Scholar]