Some mismatch repair activities in Escherichia coli.

Abstract

Heterozygous bacteriophage A DNA molecules, whose replication requires mismatch correction of a mutant nucleotide in the transcribed strand, provide an assay for localized mismatch repair in Escherichia coli. We describe two systems: one removes the A in C-A or G-A mismatches and the other removes one or the other C in a C C mismatch. Mutations disabling the first system result in a mutator phenotype that may be identical to mutY. Investigation of the products present in infective centers of bacteria transfected with artificially constructed heteroduplex DNA molecules of bacteriophage A has provided evidence for the mode of action of two mismatch repair systems in E. coli (5, 6). One of these, the adenine methylationdirected mismatch repair system, has been shown to play an important role in replication fidelity by repairing errors in a newly replicated DNA strand, distinguishing that strand by the absence of methylation at GATC sequences. This repair process directs the replacement of long tracts of the undermethylated strand (several kilobases) when a base pair mismatch is present (7). Some of the functions repaired for this mismatch repair system are encoded by mutL, mutS, mutH, and mutU (uvrD) (8). A localized repair activity became evident when the methyl-directed mismatch repair system was disabled as a result of mutations in mutH or mutU (5). This localized repair results in separation of very closely linked markers, requires the functions mutL and mutS, is independent of adenine methylation, efficiently corrects the T of G-T mismatches resulting from a C to T transition mutation in the inner C in CC(A/T)G sites (6), and is similar to the very short patch repair described by Lieb (9, 10).Serendipitous evidence of additional localized mismatch repair (11) suggested a strategy that allows the investigation of repair capacities, one mismatch at a time. DNA is isolated from phage harboring conditional (amber) mutations in functions essential for DNA replication, the strands are separated, and complementary strands from each of two different mutants are hybridized. The heteroduplex molecules are packaged in vitro and the assembled phage can be plated under permissive conditions, to determine the phage yield, or on hosts that do not suppress the amber mutations. In the latter case, plaque formation requires repair of the mutant nucleotide on the transcribed strand, without co-correction of the neighboring wild-type nucleotide that is, in turn, mismatched with a mutant nucleotide on the untranscribed strand. Thus, plaque formation reflects repair of a particular mismatch. This strategy has revealed the presence of two mismatch repair capabilities present in E. coli. One of these functions removes the A of C-A and G-A mismatches and the other corrects a C in a C C mismatch. When the A removal function is disabled, the bacteria display a mutator phenotype.

DNA glycosylases in the base excision repair of DNA

“…An E. coli DNA mismatch glycosylase (MutY) that removes adenine from A\G mismatches was originally identified as a gene that prevented C : G A : T transversion mutations [93,94]. The mutator locus was designated mutY, and the repair activity was found to be independent of the methylation state of the DNA [94,95].…”

“…The mutator locus was designated mutY, and the repair activity was found to be independent of the methylation state of the DNA [94,95]. mutY encodes a DNA glycosylase of 36 kDa which, in addition to excision of A opposite G and C, also removes A opposite the oxidized purines 8-oxoG and 7,8-dihydro-8-oxoadenine (8-oxoA) [96].…”

DNA repair glycosylases with a [4Fe–4S] cluster: A redox cofactor for DNA-mediated charge transport?

“…MutY, structurally similar to Endo III [18][19][20][21], is another BER glycosylase that contains a [4Fe-4S] cluster [20]. However, MutY instead removes adenine from 8-oxo-guanine:adenine mispairs [22][23][24][25][26][27][28][29][30][31][32][33][34].…”

Mutations in OGG1, a gene involved in the repair of oxidative DNA damage, are found in human lung and kidney tumours

“…The presence of 8-OxoG in DNA has been shown to be mutagenic since, while this lesion does not impede DNA chain elongation, it preferentially pairs with adenine during in vitro DNA synthesis (Shibutani et al, 1991). The biological incidence of the presence of 8-OxoG in DNA has been unveiled by the study of two genes in E. coli, fpg (mutM) and mutY (micA) which code for DNA glycosylases that cooperate to prevent the mutagenic e ects of 8-OxoG in DNA (Boiteux et al, 1987;Cabrera et al, 1988;Radicella et al, 1988;Nghiem et al, 1988;Au et al, 1989). Inactivation of either gene leads to a spontaneous mutator phenotype characterized by the exclusive increase in GC to TA transversions (Michaels and Miller, 1992;Grollman and Moriya, 1993;Boiteux and Laval, 1997).…”