Mismatch repair during pneumococcal transformation of small deletions produced by site-directed mutagenesis

Gasc, Anne-Marie; Garcı́a, Pedro; Baty, Daniel; Sicard, A M

doi:10.1007/bf00325708

Cited by 17 publications

(15 citation statements)

References 19 publications

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“…Tentative mismatch ranking as a function of decreasing repair efficiency is G/T = A/C = G/G > C/T > A/A > T/T > A/G; no evidence for repair of C/C has been obtained (15). The Hex system also functions in the correction of short insertions and deletions (9,14). Similar specificity of repair has been reported for two other generalized mismatch repair systems, the Mut system of Escherichia coli (9,23,28,46), and the PMS system of Saccharomyces cerevisiae (3-5, 24, 51).…”

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confidence: 55%

Mismatch repair genes of Streptococcus pneumoniae: HexA confers a mutator phenotype in Escherichia coli by negative complementation

et al. 1991

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DNA repair systems able to correct base pair mismatches within newly replicated DNA or within heteroduplex molecules produced during recombination are widespread among living organisms. Evidence that such generalized mismatch repair systems evolved from a common ancestor is particularly strong for two of them, the Hex system of the gram-positive Streptococcus pneumonwae and the Mut system of the gram-negative Escherichia coli and Salmonella typhimurium. The homology existing between HexA and MutS and between HexB and MutL prompted us to investigate the effect of expressing hex genes in E. coli. Complementation of mutS or mutL mutations, which confer a mutator phenotype, was assayed by introducing on a multicopy plasmid the hexA and hexB genes, under the control of an inducible promoter, either individually or together in E. coli strains. No decrease in mutation rate was conferred by either hexA or hexB gene expression.However, a negative complementation effect was observed in wild-type E. coli cells: expression of hexA resulted in a typical Mut-mutator phenotype. hexB gene expression did not increase the mutation rate either individually or in conjunction with hexA. Since expression of hexA did not affect the mutation rate in mutS mutant cells and the hexA-induced mutator effect was recA independent, it is concluded that this effect results from inhibition of the Mut system. We suggest that HexA, like its homolog MutS, binds to mismatches resulting from replication errors, but in doing so it protects them from repair by the Mut system. In agreement with this hypothesis, an increase in mutS gene copy number abolished the hexA-induced mutator phenotype. HexA protein could prevent repair either by being unable to interact with Mut proteins or by producing nonfunctional repair complexes.

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confidence: 55%

Mismatch repair genes of Streptococcus pneumoniae: HexA confers a mutator phenotype in Escherichia coli by negative complementation

et al. 1991

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“…Insertions and deletions that were more than four bases long were not repaired in other transformable species in which MMRdeficient mutants were examined, including Acinetobacter species (89), S. pneumoniae (22), and Bacillus subtilis (48).…”

Section: ϫ4mentioning

confidence: 99%

Impact of mutS Inactivation on Foreign DNA Acquisition by Natural Transformation in Pseudomonas stutzeri

Meier

Wackernagel

2005

J Bacteriol

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In prokaryotic mismatch repair the MutS protein and its homologs recognize the mismatches. The mutS gene of naturally transformable Pseudomonas stutzeri ATCC 17587 (genomovar 2) was identified and characterized. The deduced amino acid sequence (859 amino acids; 95.6 kDa) displayed protein domains I to IV and a mismatchbinding motif similar to those in MutS of Escherichia coli. A mutS::aac mutant showed 20-to 163-fold-greater spontaneous mutability. Transformation experiments with DNA fragments of rpoB containing single nucleotide changes (providing rifampin resistance) indicated that mismatches resulting from both transitions and transversions were eliminated with about 90% efficiency in mutS ؉ . The mutS ؉ gene of strain ATCC 17587 did not complement an E. coli mutant but partially complemented a P. stutzeri JM300 mutant (genomovar 4). The declining heterogamic transformation by DNA with 0.1 to 14.6% sequence divergence was partially alleviated by mutS::aac, indicating that there was a 14 to 16% contribution of mismatch repair to sexual isolation. Expression of mutS ؉ from a multicopy plasmid eliminated autogamic transformation and greatly decreased heterogamic transformation, suggesting that there is strong limitation of MutS in the wild type for marker rejection. Remarkably, mutS::aac altered foreign DNA acquisition by homology-facilitated illegitimate recombination (HFIR) during transformation, as follows: (i) the mean length of acquired DNA was increased in transformants having a net gain of DNA, (ii) the HFIR events became clustered (hot spots) and less dependent on microhomologies, which may have been due to topoisomerase action, and (iii) a novel type of transformants (14%) had integrated foreign DNA with no loss of resident DNA. We concluded that in P. stutzeri upregulation of MutS could enforce sexual isolation and downregulation could increase foreign DNA acquisition and that MutS affects mechanisms of HFIR.In all organisms repair of DNA is an essential process for maintaining DNA integrity and for avoiding mutations. Misincorporated bases remaining after DNA replication or spontaneous base modification in DNA produce mismatches which are repaired by an excision-type mechanism provided by the mismatch repair (MMR) system (11, 56). MMR proteins were first identified in Streptococcus pneumoniae, and the best-characterized MMR proteins are those in Escherichia coli (11,55). In prokaryotes MutS initiates the repair by recognition and binding to the mismatch; this is followed by a search together with MutL on both sides of the mismatch for a site from where excision can be initiated (30). The ubiquity of MutS homologs in all three biological kingdoms (19) underscores the importance of MutS in maintaining the genetic stability of cellular genomes (26). In bacteria loss of the mismatch repair capacity results in mutator strains with increased spontaneous mutation frequencies (23). Such mutator strains have been found among environmental, commensal, and pathogenic isolates of Pseudomonas aeruginosa (59), E. c...

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“…These differences represent the efficiency with which these mutations are processed by the mismatch repair (MMR) system [15]–[21]. Deletions of 3 bp or shorter also act as low efficiency markers that are subject to MMR [14], [22], [23], but those of 5 bp or longer tend to be transferred at a relatively higher rate due to less effective repair by MMR [12]–[14], [23]–[25].…”

Section: Introductionmentioning

confidence: 99%

A High-Resolution View of Genome-Wide Pneumococcal Transformation

Croucher

Harris²,

Barquist³

et al. 2012

PLoS Pathog

101

161

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Transformation is an important mechanism of microbial evolution through which bacteria have been observed to rapidly adapt in response to clinical interventions; examples include facilitating vaccine evasion and the development of penicillin resistance in the major respiratory pathogen Streptococcus pneumoniae . To characterise the process in detail, the genomes of 124 S. pneumoniae isolates produced through in vitro transformation were sequenced and recombination events detected. Those recombinations importing the selected marker were independent of unselected events elsewhere in the genome, the positions of which were not significantly affected by local sequence similarity between donor and recipient or mismatch repair processes. However, both types of recombinations were sometimes mosaic, with multiple non-contiguous segments originating from the same molecule of donor DNA. The lengths of the unselected events were exponentially distributed with a mean of 2.3 kb, implying that recombinations are stochastically resolved with a fixed per base probability of 4.4×10 −4 bp −1 . This distribution of recombination sizes, coupled with an observed under representation of large insertions within transferred sequence, suggests transformation has the potential to reduce the size of bacterial genomes, and is unlikely to act as an efficient mechanism for the uptake of accessory genomic loci.

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Mismatch repair during pneumococcal transformation of small deletions produced by site-directed mutagenesis

Cited by 17 publications

References 19 publications

Mismatch repair genes of Streptococcus pneumoniae: HexA confers a mutator phenotype in Escherichia coli by negative complementation

Mismatch repair genes of Streptococcus pneumoniae: HexA confers a mutator phenotype in Escherichia coli by negative complementation

Impact of mutS Inactivation on Foreign DNA Acquisition by Natural Transformation in Pseudomonas stutzeri

A High-Resolution View of Genome-Wide Pneumococcal Transformation

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