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1.
Björn Rydberg 《Molecular & general genetics : MGG》1977,152(1):19-28
Summary Bromouracil mutagenesis was studied in several strains of E. coli in combination with measurement of incorporation of bromouracil in DNA. For levels below 10% total replacement of bromouracil for thymine, mutagenesis was negligible compared with higher levels of incorporation. Such a nonlinear response occurred both when the bromouracil was evenly distributed over the genome and when a small proportion of the genome was highly substituted. Also, the mutation frequency could be drastically lowered by amino acid starvation following bromouracil incorporation. These observations suggest the involvement of repair phenomena. Studies of mutagenesis in recA
– and uvrA
– mutants, as well as studies of prophage induction, did not support an error prone repair pathway of mutagenesis. On the other hand, uvrD
– and uvrE
– mutants, which are deficient in DNA mismatch repair, had much increased mutation frequencies compared with wild type cells. The mutagenic action of bromouracil showed specificity under the conditions used, as demonstrated by the inability of bromouracil to revert an ochre codon that was easily revertable by ultraviolet light irradiation. The results are consistent with a mechanism of bromouracil mutagenesis involving mispairing, but suggest that the final mutation frequencies depend on repair that removes mismatched bases. 相似文献
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Saturation of mismatch repair in the mutD5 mutator strain of Escherichia coli. 总被引:5,自引:3,他引:5
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The mutD (dnaQ) gene of Escherichia coli codes for the proofreading activity of DNA polymerase III. The very strong mutator phenotype of mutD5 strains seems to indicate that their postreplicational mismatch repair activity is also impaired. We show that the mismatch repair system of mutD5 strains is functional but saturated, presumably by the excess of DNA replication errors, since it is recovered by inhibiting chromosomal DNA replication. This recovery depends on de novo protein synthesis. 相似文献
4.
The Escherichia coli mismatch repair system greatly improves DNA replication fidelity by repairing single mispaired and unpaired bases in newly synthesized DNA strands. Transient undermethylation of the GATC sequences makes the newly synthesized strands susceptible to mismatch repair enzymes. The role of unmethylated GATC sequences in mismatch repair was tested in transfection experiments with heteroduplex DNA of phage phi 174 without any GATC sequence or with two GATC sequences, containing in addition either a G:T mismatch (Eam+/Eam3) or a G:A mismatch (Bam+/Bam16). It appears that only DNA containing GATC sequences is subject to efficient mismatch repair dependent on E. coli mutH, mutL, mutS and mutU genes; however, also in the absence of GATC sequence some mut-dependent mismatch repair can be observed. These observations suggest that the mismatch repair enzymes recognize both the mismatch and the unmethylated GATC sequence in DNA over long distances. The presence of GATC sequence(s) in the substrate appears to be required for full mismatch repair activity and not only for its strand specificity according to the GATC methylation state. 相似文献
5.
Colicchio R Pagliarulo C Lamberti F Vigliotta G Bruni CB Alifano P Salvatore P 《DNA Repair》2006,5(12):1428-1438
Several invasive serogroup B meningococcal strains phylogenetically related to the lineage III (ET-24) exhibited a mutator phenotype as shown by mutagenicity assay using rifampicin-resistance as a selection marker. Hypermutation was associated to the presence of defective mutL alleles that were genetically characterized. Interestingly, the mutator phenotype was suppressed when a non-functional recB(ET-37) allele, derived from ET-37 meningococcal strains, replaced the functional recB allele in a lineage III strain. In contrast, the same gene replacement did not affect mutation frequencies in a mismatch repair-proficient strain. These results suggested that in MutL-deficient strains spontaneous mutations mostly arise from post-replicative DNA synthesis associated to the activity of the RecBCD recombination pathway. 相似文献
6.
Specificity of Escherichia coli mutD and mutL mutator strains 总被引:10,自引:0,他引:10
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. 相似文献
7.
Methyl-directed DNA mismatch repair in Escherichia coli 总被引:5,自引:0,他引:5
Some of the molecular aspects of methyl-directed mismatch repair in E. coli have been characterized. These include: mismatch recognition by mutS protein in which different mispairs are bound with different affinities; the direct involvement of d(GATC) sites; and strand scission by mutH protein at d(GATC) sequences with strand selection based on methylation of the DNA at those sites. In addition, communication over a distance between a mismatch and d(GATC) sites has been implicated. Analysis of mismatch correction in a defined system (Lahue et al., unpublished) should provide a direct means to further molecular aspects of this process. 相似文献
8.
Redundant exonuclease involvement in Escherichia coli methyl-directed mismatch repair. 总被引:4,自引:0,他引:4
M Viswanathan V Burdett C Baitinger P Modrich S T Lovett 《The Journal of biological chemistry》2001,276(33):31053-31058
Previous biochemical analysis of Escherichia coli methyl-directed mismatch repair implicates three redundant single-strand DNA-specific exonucleases (RecJ, ExoI, and ExoVII) and at least one additional unknown exonuclease in the excision reaction (Cooper, D. L., Lahue, R. S., and Modrich, P. (1993) J. Biol. Chem. 268, 11823-11829). We show here that ExoX also participates in methyl-directed mismatch repair. Analysis of the reaction with crude extracts and purified components demonstrated that ExoX can mediate repair directed from a strand signal 3' of a mismatch. Whereas extracts of all possible single, double, and triple exonuclease mutants displayed significant residual mismatch repair, extracts deficient in RecJ, ExoI, ExoVII, and ExoX exonucleases were devoid of normal repair activity. The RecJ(-) ExoVII(-) ExoI(-) ExoX(-) strain displayed a 7-fold increase in mutation rate, a significant increase, but less than that observed for other blocks of the mismatch repair pathway. This elevation is epistatic to deficiency for MutS, suggesting an effect via the mismatch repair pathway. Our other work (Burdett, V., Baitinger, C., Viswanathan, M., Lovett, S. T., and Modrich, P. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 6765-6770) suggests that mutants are under-recovered in the exonuclease-deficient strain due to loss of viability that is triggered by mismatched base pairs in this genetic background. The availability of any one exonuclease is enough to support full mismatch correction, as evident from the normal mutation rates of all triple mutants. Because three of these exonucleases possess a strict polarity of digestion, this suggests that mismatch repair can occur exclusively from a 3' or a 5' direction to the mismatch, if necessary. 相似文献
9.
E M Witkin 《Microbiological reviews》1976,40(4):869-907
10.
Isolation of conditional lethal mutator mutants of Escherichia coli by localized mutagenesis. 总被引:2,自引:2,他引:2
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By using localized mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine, we isolated 39 temperature-sensitive growth mutants that exhibited high mutability when the bacteria were grown at the permissive temperature. Two of the mutations, dnaQ186 and dnaQ231, were shown to be new alleles of the dnaQ gene by genetic mapping and complementation tests with the dnaQ49 mutation previously isolated. They shared common properties with the dnaQ49 strain, but their mutator activity was not temperature dependent. The dnaQ mutants exhibited increased sensitivity to inhibitors of DNA gyrase and to DNA intercalating and alkylating agents. 相似文献
11.
Summary We introduced the dnaE486 and polC74 mutations (which are associated with decreased DNA polymerase III replication fidelity) into excision defective Escherichia coli strains with varying SOS responses. These mutations increased the UV-induced frequency of base pair substitution mutations in all strains tested, except recA430 and umuC122 derivatives. This UV mutator effect therefore requires expression of the SOS error-prone repair system. In recA441 lexA51 strains where the SOS system is constitutively expressed, the UV mutator effect of the dnaE alleles was similar in relative terms (though greater in absolute terms). Since these dnaE alleles decrease rather than increase survival after UV it is argued that they promote a burst of untargeted mutations close to UV photoproducts (hitch-hiking mutations) rather than increase the number of translesion synthesis events. The fact that there was no UV mutagenesis in dnaE486 umuC122 or polC74 umuC122 strains indicates that infidelity associated with these dnaE alleles did not of itself enable translesion synthesis to occur. The spontaneous mutator effect conferred by dnaE486 and polC74 was not affected by umuC122 or recA430 indicating that it is not dependent upon error-prone repair ability. In recA441 lexA51 bacteria, where SOS error-prone repair is constitutively induced, the mutator effect of dnaE486 was greater and was largely blocked by umuC122. It is suggested that spontaneously occurring cryptic lesions that are themselves unable to induce the SOS system are subject to translesion synthesis under these conditions and trigger a burst of hitch-hiking mutations that are therefore effectively umuC dependent. 相似文献
12.
H S Murphy V A Palejwala M S Rahman P M Dunman G Wang M Z Humayun 《Journal of bacteriology》1996,178(23):6651-6657
Mutagenesis at 3,N4-ethenocytosine (epsilonC), a nonpairing mutagenic lesion, is significantly enhanced in Escherichia coli cells pretreated with UV, alkylating agents, or H2O2. This effect, termed UVM (for UV modulation of mutagenesis), is distinct from known DNA damage-inducible responses, such as the SOS response, the adaptive response to alkylating agents, or the oxyR-mediated response to oxidative agents. Here, we have addressed the hypothesis that UVM results from transient depletion of a mismatch repair activity that normally acts to reduce mutagenesis. To test whether the loss of mismatch repair activities results in the predicted constitutive UVM phenotype, E. coli cells defective for methyl-directed mismatch repair, for very-short-patch repair, or for the N-glycosylase activities MutY and MutM were treated with the UVM-inducing agent 1-methyl-3-nitro-1-nitrosoguanidine, with subsequent transfection of M13 viral single-stranded DNA bearing a site-specific epsilonC lesion. Survival of the M13 DNA was measured as transfection efficiency, and mutation fixation at the lesion was characterized by multiplex sequencing technology. The results showed normal UVM induction patterns in all the repair-defective strains tested. In addition, normal UVM induction was observed in cells overexpressing MutH, MutL, or MutS. All strains displayed UVM reactivation, the term used to describe the increased survival of epsilonC-containing DNA in UVM-induced cells. Taken together, these results indicate that the UVM response is independent of known mismatch repair systems in E. coli and may thus represent a previously unrecognized misrepair or misreplication pathway. 相似文献
13.
Synergistic effect of an Escherichia coli mutator gene on mutagenesis by ultraviolet radiation and by alkylating agents 总被引:3,自引:0,他引:3
R F Hill 《Mutation research》1972,14(1):27-31
E. coli strains differing in a gene responsible for high spontaneous mutability (mut HI) were compared for their mutability by UV radiation and by the alkylating agents ethyl methanesulfonate and methyl methanesulfonate. All three exogenous mutagenic agents induced significantly higher frequencies of mutants with impaired carbohydrate-fermenting ability when the mutator allele rather than the wild-type allele was present. Thus the mut HI gene product possibly increases the probability of replication error due to alterations in the structure of the template strand of DNA. An attempt to detect an synergistic effect for UV-induced suppressor mutations was unsuccessful. The failure may have been due to the particular method used for scoring this type of mutation. 相似文献
14.
The extreme mutator effect of Escherichia coli mutD5 results from saturation of mismatch repair by excessive DNA replication errors. 总被引:16,自引:0,他引:16
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Escherichia coli mutator mutD5 is the most potent mutator known. The mutD5 mutation resides in the dnaQ gene encoding the proofreading exonuclease of DNA polymerase III holoenzyme. It has recently been shown that the extreme mutability of this strain results, in addition to a proofreading defect, from a defect in mutH, L, S-encoded postreplicational DNA mismatch repair. The following measurements of the mismatch-repair capacity of mutD5 cells demonstrate that this mismatch-repair defect is not structural, but transient. mutD5 cells in early log phase are as deficient in mismatch repair as mutL cells, but they become as proficient as wild-type cells in late log phase. Second, arrest of chromosomal replication in a mutD5-dnaA(Ts) strain at a nonpermissive temperature restores mismatch repair, even from the early log phase of growth. Third, transformation of mutD5 strains with multicopy plasmids expressing the mutH or mutL gene restores mismatch repair, even in rapidly growing cells. These observations suggest that the mismatch-repair deficiency of mutD strains results from a saturation of the mutHLS-mismatch-repair system by an excess of primary DNA replication errors due to the proofreading defect. 相似文献
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17.
Singlet oxygen ((1)O(2)) is a product of several biological processes and can be generated in photodynamic therapy, through a photosensitization type II mechanism. (1)O(2) is able to interact with lipids, proteins and DNA, leading to cell killing and mutagenesis, and can be directly involved with degenerative processes such as cancer and aging. In this work, we analyzed the cytotoxicity and mutagenesis induced after direct treatment of wild type and the DNA repair fpg and/or mutY deficient Escherichia coli strains with disodium 3,3'-(1,4-naphthylidene) diproprionate endoperoxide (NDPO(2)), which releases (1)O(2) by thermodissociation. The treatment induced cell killing and mutagenesis in all strains, but the mutY strain showed to be more sensitive. These results indicate that even (1)O(2) generated outside bacterial cells may lead to DNA damage that could be repaired by pathways that employ MutY protein. As (1)O(2) is highly reactive, its interaction with cell membranes may generate secondary products that could react with DNA, leading to mutagenic lesions. 相似文献
18.
19.
Influence of GATC sequences on Escherichia coli DNA mismatch repair in vitro. 总被引:2,自引:4,他引:2
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A L Lu 《Journal of bacteriology》1987,169(3):1254-1259
The effect of the number and position of DNA adenine methylation (dam) sites, i.e., d(GATC) sequences, on mismatch repair in Escherichia coli was investigated. The efficiency of repair was measured in an in vitro assay which used an f1 heteroduplex containing a G/T mismatch within the single EcoRI site. Both an increase in the number of dam sites and a shortened distance between dam site and mismatched site increased the efficiency of mismatch repair. The sequences adjacent to d(GATC) also affected the efficiency of methylation-directed mismatch repair. Furthermore, heteroduplexes with one extra dam site located close to either the 5' or 3' end of the excised base increased the repair efficiency to about the same extent. The findings suggest that the mismatch repair pathway has no preferred polarity. 相似文献