Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SOS Response, Genetics”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed1993

Chemically altered apurinic sites in phi X174 DNA give increased mutagenesis in SOS-induced E. coli.

Single-strand DNA from bacteriophage phi X174 am3 is treated with mild acid and heat to produce increasing numbers of apurinic sites per molecule. Samples are assayed, either directly or after additional chemical reactions, by electroporation into the recipient E. coli strain HF4714(su-1+). Modified apurinic sites are produced by reactions with O-methyl- or O-benzyl-hydroxylamine, and reduced apurinic sites by reactions with sodium borohydride. Reversion mutation frequencies are significant only if the recipient strain is SOS-induced (by growth after UV irradiation). A simple apurinic site at the target gives rise to mutation (a transversion) with a probability of 0.07, while the modified or reduced apurinic site has a mutagenic efficiency of 0.22-0.27 or 0.29, respectively. The open ring form of deoxyribose may account for the 3-4-fold increased mutagenicity with altered apurinic lesions. Also considered are effects by temperature and cyclobutane pyrimidine dimers on mutagenicity and the relatively invariant survival curves that obtain regardless of chemical alterations at the apurinic sites and/or SOS induction.

Bacteriophage phi X 174↗
PubMed1993

Inhibition and induction of SOS responses in Escherichia coli by cobaltous chloride.

Mutagenesis induced by several genotoxic agents has been reported to be inhibited by cobaltous chloride. In order to study the effects of this metal in some SOS functions we evaluated mutagenesis, lysogenic induction and phage reactivation in Escherichia coli cells treated with CoCl2. We detected that cobaltous chloride, when present in the plating medium, was able to block mutagenesis and lysogenic induction promoted by UV irradiation. We also found that CoCl2 blocked protein synthesis, so we propose that this effect can be responsible for the antimutagenic and antilysogenic effects of this metal. On the other hand, if the cells were treated for a short period of time with CoCl2, in the absence of Mg, we observed that cobaltous chloride per se was able to promote lysogenic induction as well as to enhance the phage reactivation induced by UV irradiation. We conclude that depending on experimental conditions, cobaltous chloride may act either as an inhibitor or as an inducer of the SOS functions.

Antimutagenic Agents↗
PubMed1993

Antimutagenic effects of N-methyl-valyl-amiclenomycin (BA-2) isolated from the metabolites of Streptomyces sp.

A novel antimutagenic factor, BA-2, active against UV-induced mutagenesis in Escherichia coli WP2 was isolated from the metabolites of Streptomyces sp. strain AJ9455. BA-2 also suppressed mutations induced by 4-nitroquinoline N-oxide (4-NQO) and furylfuramide (AF-2) in E. coli WP2s (uvrA) without any decrease of cellular viability. BA-2 strongly inhibited the UV induction of SOS repair functions when it was monitored by beta-galactosidase activity expressed from the sulA::lacZ fusion gene of strain PQ37. It is assumed that the antimutagenic effect of BA-2 on mutagenesis induced by UV, 4-NQO or AF-2 was the result of inhibition of induction of the inducible error-prone SOS repair. The structure of BA-2 was considered to be N-methyl-valyl-amiclenomycin, and the structural unit of 4-amino-2,5-cyclohexadiene must be essential for the antimutagenic activity, since deamination by heating results in the loss of antimutagenic activity of BA-2.

Aminobutyrates↗
PubMed1994

DNA sequence analysis of spontaneous and gamma-radiation (anoxic)-induced lacId mutations in Escherichia coli umuC122::Tn5: differential requirement for umuC at G.C vs. A.T sites and for the production of transversions vs. transitions.

Escherichia coli umuC122::Tn5 cells were gamma-irradiated (137Cs, 750 Gy, under N2), and lac-constitutive mutants were produced at 36% of the wild-type level (the umuC strain was not deficient in spontaneous mutagenesis, and the mutational spectrum determined by sequencing 263 spontaneous lacId mutations was very similar to that for the wild-type strain). The specific nature of the umuC strain's partial radiation mutability was determined by sequencing 325 radiation-induced lacId mutations. The yields of radiation-induced mutation classes in the umuC strain (as a percentage of the wild-type yield) were: 80% for A.T-->G.C transitions, 70% for multi-base additions, 60% for single-base deletions, 53% for A.T-->C.G transversions, 36% for G.C-->A.T transitions, 25% for multi-base deletions, 21% for A.T-->T.A transversions, 11% for G.C-->C.G transversions, 9% for G.C-->T.A transversions, and 0% for multiple mutations. Based on these deficiencies and other factors, it is concluded that the umuC strain is near-normal for A.T-->G.C. transitions, single-base deletions and possibly A.T-->C.G transversions; is generally deficient for mutagenesis at G.C sites and for transversions, and is grossly deficient in multiple mutations. Damage at G.C sites seems more difficult for translesion DNA synthesis to bypass than damage at A.T sites, and especially when trying to produce a transversion. The yield of G.C-->A.T transitions in the umuC strain (36% of the wild-type level) argues that abasic sites are involved in no more than 64% of gamma-radiation-induced base substitutions in the wild-type strain. Altogether, these data suggest that the UmuC and UmuD' proteins facilitate, rather than being absolutely required for, translesion DNA synthesis; with the degree of facilitation being dependent both on the nature of the noncoding DNA damage, i.e., at G.C vs. A.T sites, and on the nature of the misincorporated base, i.e., whether it induces transversions or transitions.

Bacterial Proteins↗
PubMed1994

Damage and mutagenesis of E. coli and bacteriophage lambda induced by oxathiolane and aziridinyl steroids.

lambda-Escherichia coli complexes exhibited remarkable sensitivity to the treatment with test steroidal derivatives in the presence of Cu(II). The decline in plaque-forming units after steroid treatment was more pronounced in complexes with some of the radiation repair-defective mutants of E. coli K-12, i.e., recA, lexA and polA, as compared to uvrA and wild-type strains. The red gene of lambda phage and recA gene of E. coli seem to have a complementary effect on the steroid-induced lesions. An enhanced level of mutagenesis was observed when steroid-treated E. coli cells were transformed with steroid-treated pBR322 plasmid DNA. A remarkable degree of c mutation was also observed when steroid I-treated phage particles were allowed to adsorb on steroid-treated wild-type bacteria. Moreover, the oxathiolane steroid treatment of lambda cI857-E. coli lysogen resulted in prophage induction in nutrient broth even at 32 degrees C. Thus on the basis of these results, the role of SOS repair system in steroid-induced mutagenesis and repair of DNA lesions in E. coli and bacteriophage lambda has been suggested.

Aziridines↗
PubMed1994

Processing of MucA protein is required for spontaneous and benzo[a]pyrene-induced reversion of the Escherichia coli trpA23 missense mutation by G.C-T.A transversions: effect of a deficiency in the MutY DNA glycosylase.

We have studied the influence of the processing of MucA protein on the occurrence of base substitution mutations. Escherichia coli strains carrying the trpA23 missense mutation and having a full deletion of the chromosomal umuD/C operon were transformed with plasmids encoding the MucB protein together with either wild-type MucA or the nonprocessable MucA202 protein. The efficient reversion of the trpA23 allele by G.C-T.A transversions in benzo[a]pyrene (B[a]P)-treated cells required the function of a matured MucA protein. This processed protein was also necessary for the occurrence of G.C-T.A transversions targeted at spontaneous DNA lesions and for the SOS mutator effect dependent on the constitutive coprotease activity of the RecA730 protein. In contrast, G.C-T.A transversions reverting trpA23 were spontaneously generated by an SOS-independent mechanism in cells deficient in the MutY DNA glycosylase.

Bacterial Proteins↗
PubMed1994

Autoregulation and kinetics of induction of the Rhizobium phaseoli recA gene.

A fusion between the recA gene of Rhizobium phaseoli and the lacZ gene was constructed in vitro and cloned in a mini-Tn5 transposon derivative to obtain chromosomal insertions which make it possible to quantitatively examine their transcriptional regulation in both R. phaseoli and E. coli. Likewise, and by insertion of a spectinomycin-resistance gene cassette into the recA gene of R. phaseoli and subsequent marker exchange, a RecA- derivative of this bacterial species has been obtained. Analysis of this recA-lacZ fusion showed that it was inducible by DNA damage in the RecA+ strain of R. phaseoli but not in the RecA- mutant. On the other hand, the recA-lacZ fusion of R. phaseoli was not induced in DNA-damaged RecA+ cells of E. coli. Furthermore, the range of UV doses which give rise to dose dependence in the induction of its respective recA genes is different in R. phaseoli from that in E. coli.

Cloning, Molecular↗
PubMed1994

The structural basis of the genotoxicity of nitroarenofurans and related compounds.

The CASE (Computer-Automated Structure Evaluation) methodology has been applied to an investigation of the basis of the genotoxicity (sfiA induction) of 79 nitroarenofurans and related molecules examined with the E. coli PQ37 genotoxicity assay (SOS chromotest). CASE identified 9 major activating structural fragments (biophores) responsible for the probability of genotoxicity (SAR). With respect to quantitative features, CASE identified 8 major molecular subunits related to the genotoxic potency (QSAR). Both the SAR as well as the QSAR analysis indicate that a nitro group on position 2 of the furan ring is important for activity provided one or more aromatic rings are attached to the furan ring, i.e. 2-nitrobenzofuran, 2-nitronaphthofuran, 2-nitroanthrafuran and 8-nitropyrenofuran. Additionally, a small substituent at position 3 of the furan ring, i.e. the methyl group of R7371, the ethyl group of R7427 and the butyl group of R7429, enhance the activity of 2-nitronaphtho[2,1-b]furan (R6597), whereas longer aliphatic chains decrease activity. Moreover, the activity of the nitro group at position 2 of the furan ring was increased by substitution of a methoxy group at position 7 of the R6597 structure. Additionally the n-octanol/water partition coefficient (log P) was found to be an important descriptor for the genotoxic potency in E. coli PQ37. Using the identified descriptors CASE correctly predicted the probability of genotoxicity of all of the genotoxicants and non-genotoxicants in the data base. The calculated genotoxic potency was equally good: 94% of all predicted results were within plus/minus one order of magnitude of the experimental result. Using CASE in the predictive mode, the program correctly predicted the probability of sfiA induction in E. coli of 95.8% of 24 "unknown" nitroarenofurans which were not part of the learning set (QSAR with r = 0.88-0.97).

Benzofurans↗
PubMed1994

The SOS function-inducing activity of the new nitrothiophenic derivatives in Escherichia coli.

Genotoxicity and cytotoxic effects of eight new nitrothiophenic compounds with trypanocidal activity were determined by means of the SOS Chromotest assay. Our results indicate that all nitro compounds with one aromatic ring in the R group were genotoxic without and with metabolic activation. The compounds with two aromatic rings in the R group, except for indazol-1-yl, were strongly cytotoxic but they were unable to induce SOS functions without metabolic activation. However, after metabolic activation no cytotoxic effect was observed for these compounds. The role of the nitroreductases to explain the different genotoxic responses of these nitrothiophenic derivatives is discussed.

Escherichia coli↗
PubMed1994

Regulatory processes and the origins of spontaneous mutations.

A review of information currently available about the origins of spontaneous mutational events suggests that there may be a role for known cellular control mechanisms in determining the frequencies with which such events can occur. Attention is also directed to recent findings with antimutator (dnaE) mutants of Escherichia coli which indicate that the final step involved in generating a spontaneous mutational event may be different from that involved in generating an SOS-dependent mutational event. Finally, the possible involvement of various sorts of treatments collectively referred to as stress responses (heat shock, cold shock or oxidative damage, etc.) in generating random mutations is discussed; if there is such an involvement, this may represent one way in which organisms are programmed to adapt to a wide variety of environmental challenges.

Escherichia coli↗
PubMed1994

Structure-activity studies in E. coli strains on ochratoxin A (OTA) and its analogues implicate a genotoxic free radical and a cytotoxic thiol derivative as reactive metabolites.

Ochratoxin A (OTA), its major metabolite in rodents, ochratoxin alpha, and seven structurally related substances were assayed for SOS DNA repair inducing activity in Escherichia coli strain PQ37. At concentrations of 0.1-4 mM, OTA, chloroxine, 5-chloro-8-quinolinol, 4-chloro-meta-cresol and chloroxylenol induced SOS DNA repair in the absence of an exogenous metabolic activation system. Ochratoxin B, ochratoxin alpha, 5-chlorosalicylic acid and citrinin were inactive, but all except ochratoxin alpha were cytotoxic. Thus, the presence of chlorine at C-5 appears to be one determinant of genotoxicity in these substances. Amino oxyacetic acid, an inhibitor of the cysteine conjugate beta-lyase, decreased the cytotoxicity of OTA but did not alter its genotoxic activity, suggesting the formation of a cytotoxic thiol-containing derivative. The mechanisms by which OTA and some of its active analogues induce SOS DNA repair activity was further investigated in E. coli PQ37 and in three derived strains (PQ300, OG100 and OG400), containing deletions within the oxy R regulon. The response in strain PQ37 was measured in the absence and presence of Trolox C, a water-soluble form of vitamin E. Trolox C completely quenched the genotoxicity of OTA, and the effect was similar in the mutant and wild-type strains. These results implicate an OTA-derived free radical rather than reduced oxygen species as genotoxic intermediate(s) in bacteria.

Escherichia coli↗
PubMed1995

Emodin inhibits the mutagenicity and DNA adducts induced by 1-nitropyrene.

Polygonum cuspidatum S. (PC) is frequently used as a laxative and an anticancer drug in Chinese medicine. The inhibitory effect of this herb and its component, emodin, on the direct-acting mutagenicity of 1-nitropyrene (1-NP) was examined using the Ames/microsomal test with Salmonella typhimurium TA98 and the genotoxicity of 1-NP was evaluated using the SOS chromotest with E. coli PQ37. Emodin and water extracts of PC markedly decreased the mutagenicity of 1-NP in a dose-dependent manner in both assay systems. Furthermore, emodin and the extracts of PC significantly inhibited the formation of 1-NP DNA adducts in S. typhimurium TA98 in the 32P-postlabeling study. The results suggest that PC extracts and emodin act as blocking and/or suppressing agents to reduce the direct-acting mutagenicity of 1-NP.

Antimutagenic Agents↗
PubMed1995

Detection of oxidative mutagens in strains of Escherichia coli deficient in the OxyR or MutY functions: dependence on SOS mutagenesis.

The Escherichia coli strain IC3821, a delta oxyR derivative of WP2 uvrA trpE65, was more sensitive to mutagenicity promoted by t-butyl hydroperoxide and cumene hydroperoxide than the isogenic oxyR+ control. Mutagenicity of menadione, a redox cycling quinone, was clearly detected in the delta oxyR strain, whereas only a slight mutagenic response was observed in the oxyR+ strain. Plumbagin, another quinone structurally similar to menadione, was not mutagenic to any of the strains. These mutagenic responses appeared to involve the SOS processing of oxidative DNA lesions and were mediated by MucA/B proteins more efficiently than by UmuD/C. In cells lacking mutagenesis proteins, induction of SOS-independent mutations by the two alkyl hydroperoxides required a deficiency in the MutY DNA glycosylase and was increased by the presence of the delta oxyR mutation. In contrast, the two quinones assayed were unable to induce SOS-independent mutations in the MutY-deficient strains.

Benzene Derivatives↗
PubMed1996

Global response of Escherichia coli cells to a treatment with 7-methoxy-2-nitronaphtho[2,1-b]furan (R7000), an extremely potent mutagen.

We have studied the global changes which are induced in exponentially growing cultures of Escherichia coli during treatment with 7-methoxy-2-nitronaphtho[2,1-b]furan (R7000), a very potent mutagen and inducer of the SOS response. A two-dimensional analysis of the proteins synthesized in the presence of this agent was performed. In a strain deficient in SOS induction, the expression of 24 polypeptides was found to be affected by this treatment: 14 corresponded to proteins known to be implicated in different stress responses, particularly chaperones such as DnaK and GroEL. The variation of another protein was detected for the first time in this study: transketolase I, an enzyme of intermediary metabolism which was characterized in the present work by microsequencing. In parallel, the expression of 9 other proteins, still unidentified, was modified by this nitrofuran. They represent potential candidates involved in metabolic and DNA lesions repair specific of R7000 action.

Bacterial Proteins↗
PubMed1996

Efficiency of MucAB and Escherichia coli UmuDC proteins in quinolone and UV mutagenesis in Salmonella typhimurium: effect of MucA and UmuD processing.

The role of MucAB and Escherichia coli UmuDC proteins in mutagenesis by 4-quinolone (4-Q) compared to that in UV mutagenesis has been studied in hisG428 Salmonella typhimurium strains. A low-copy plasmid carrying mucAB genes, but not umuDC, promotes reversion of the hisG428 mutation by the 4-Q ciprofloxacin. In contrast, a umuDC plasmid mediates the reversion of hisG428 by UV, although less efficiently than a mucAB one. In addition, a unique copy of mucAB genes is enough to promote UV mutagenesis, whereas, several copies of them are required to detect ciprofloxacin mutagenesis. Therefore, the mutagenic repair of quinolone damage by MucAB proteins is not a very efficient process. The presence of an umuD'C plasmid but not a mucA'B one, slightly increases the reversion of the hisG428 mutation by ciprofloxacin and this finding is further discussed. In contrast, MucA'B are still more active than UmuD'C proteins in UV mutagenesis. These results suggest that the enhanced processing of MucA compared to UmuD would not explain all functional differences between MucAB and UmuDC proteins in the error-prone DNA repair.

Anti-Infective Agents↗
PubMed1996

Construction of a new system for separate expression of mutagenesis proteins: the abilities to promote UV mutagenesis and interchangeability of MucA', MucB, SamA' and SamB proteins in Salmonella typhimurium.

The two distinct mucAB and samAB operons originally isolated from the plasmids of Salmonella typhimurium encode proteins engaged in induced mutagenesis. They represent two extreme cases among the so far characterized members of the enterobacterial umuDC family in respect to both the strength and the specificity of their effect. It is suggested that the MucA and SamA proteins are post-translationally processed to MucA' and SamA', respectively, which lack the N-terminal 25 amino acids and are the active species in mutagenesis. For the purpose of characterizing the individual activities of these proteins, we developed a new system for their SOS-independent separate and controllable expression in enterobacteria. Besides the matured forms of MucA', SamA' as well as MucB and SamB proteins we also expressed hybrid HisTag-MucA' and HisTag-SamA' proteins in which a synthetic 24 amino acid HisTag region replaces the natural 25 amino acid N-terminal leader present in the MucA and SamA precursors. In this study, we analyzed the effect of the mutagenesis proteins on the UV mutability of S. typhimurium YG5144. None of the proteins, if expressed alone, promoted UV mutagenesis. Different combinations of the proteins promoted mutagenesis to different extents in the order MucA' + MucB > SamA' + SamB > or = HisTag-MucA' + MucB > or = SamA' + MucB > MucA' + SamB > HisTag-SamA' + SamB. The mutagenesis enhancing potential of the combinations with MucB protein decreased as the expression of the proteins increased while the mutagenesis enhancing potential of the combinations with SamB protein increased together with the increase in the expression. The artificially expressed MucA' + MucB proteins were as active as their MucAB counterparts expressed from the plasmid pKM101 in promoting UV mutagenesis, but they were remarkably more efficient than their pKM101-born counterparts in promoting spontaneous mutagenesis. We conclude that the MucA'B and SamA'B proteins are partly interchangeable and the functionality of the resulting A' + B complex is largely dependent on the appropriate B-protein.

Amino Acid Sequence↗
PubMed1996

SOS-inducing ability of native and mutant microbial ribonucleases.

The results of genotoxicity testing of microbial ribonucleases from Bacillus species with different catalytic activity obtained by site-directed mutagenesis in SOS chromotest are reported. At the concentrations 0.1-1 mg/ml, the induction factor for wild-type bacillar binase, barnase and mutant Arg58Lys binase with 100% activity was found to be significantly higher than 1.5 (1.8-2.8). Mutant RNases having decreased catalytic activity (binases with replacements Lys26Ala, Arg61Gln, His101Glu) or through natural inhibitor barstar inactivated wild-type RNase exhibited no SOS-inducing potency. The ability of native bacillar RNases and mutant enzymes possessing high catalytic activity comparable with the activity of wild-type RNase to cause the SOS response indicates that genotoxicity is mediated through the probable cleavage of cellular RNA.

Bacterial Proteins↗
PubMed1996

Specificity of spontaneous and t-butyl hydroperoxide-induced mutations in delta oxyR strains of Escherichia coli differing with respect to the SOS mutagenesis proficiency and to the MutY and MutM functions.

Mutations induced by oxidative DNA damage appear to occur by two pathways, differing in their dependence on SOS mutagenesis. We have analysed the specificity of mutations produced by each pathway. Base substitutions generating extragenic suppressors were characterized in Trp+ revertants of Escherichia coli strains carrying the trpE65 ochre mutation, which were hypersensitive to oxidative mutagenesis due to a deletion of the oxyR gene. In strain IC3821, containing MucA/B proteins and therefore proficient for SOS mutagenesis, the more frequently scored base substitutions, either spontaneous or induced by t-butyl hydroperoxide (BuOOH), were T:A-A:T transversions, followed by G:C-A:T transitions, while the frequency of G:C-T:A transversions was lower. This SOS-dependent mutability could be promoted by abasic sites. In strains IC3894 (mutY) and IC3981 (mutY mutM), lacking mutagenesis proteins, SOS-independent revertants arose almost exclusively via G:C-T:A transversions probably derived from oxidatively damaged 8-oxoguanine/adenine mispairs. Formation of these mispairs in IC3894 and IC3981 would be enhanced by BuOOH treatment since it caused a significant increase in the revertant number. Strains IC3894 and IC3981 could have a complementary role to that of IC3821 to analyse the mutagenicity and the mutational specificity of oxidants.

DNA Glycosylases↗