PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “SOS Response, Genetics”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 451 records · Page 25Linked to original sources
PubMed1992

Genotoxicity of fungi evaluated by SOS microplate assay.

By an introduction of sodium dodecylsulfate for cell lysis and immunomicroplate for mass assay, the modified SOS microplate assay method was established and applied for the evaluation of genotoxicity of mycotoxins and fungal cultures. Among 20 mycotoxins, the carcinogenic dihydrobisfuranoids such as aflatoxin B1, sterigmatocystin, and versicolorin A were positive in the presence of the activation system. While, the carcinogenic anthraquinones and lactones such as luteoskyrin, rugulosin, ochratoxin A, patulin, and citrinin were negative. The survey on genotoxic fungi revealed that, among 15 fungal isolates Aspergillus versicolor, Emericella acristata, and others were positive. Additional survey on 265 fungal isolates have revealed that various Aspergillus genera such as A. flavus, A. parasiticus, A. ustus, A. nidulans, and others were positive for SOS induction, along with several isolates of Fusarium moniliforme. The chemical analysis revealed that the dihydrobisfuranoids such as aflatoxin B1, and sterigmatocystin were the major genotoxic metabolites of several Aspergillus species. The SOS microplate assay system is a simple and rapid procedure for the mass screening of genotoxic fungi, particularly of the dihydrobisfuranoids-producing strains.

Animals↗
PubMed2004

Potent antioxidative and antigenotoxic activity in aqueous extract of Japanese rice bran--association with peroxidase activity.

To estimate the preventive potential of Japanese rice bran (Oryza sativa japonica) against the oxygen radical-related chronic diseases such as cardio-vascular diseases and cancer, antioxidative and antigenotoxic activities of the rice bran extracts were analyzed by using assay systems for lipid peroxidation and genotoxin-induced umu gene expression. When effects of the rice bran extracts under different extraction conditions on hydroperoxide generation from auto-oxidized linoleic acid were examined using aluminum chloride method, the water extract showed strong antioxidant activity, but the methanol and acetone extracts did not exhibit significant activity. The water extract of rice bran was divided into the ethanol-precipitable (EP) and supernatant fractions, and EP fraction showed the dominant antioxidant activity, but the supernatant fraction did not exhibit significant antioxidant activity. When the effect of EP fraction on umu C gene expression in SOS response associated with DNA damage in Salmonella typhimurium (TA 1535/pSK 1002) induced by 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) was analyzed, it showed a dose-dependent suppressive activity against Trp-P-1-induced umu C gene expression. The bio-chemical analysis of EP fraction indicates that the major antioxidative and antigenotoxic activity of EP fraction is associated with a proteinous component with the molecular weight of more than 30 KDa. As a possible active principle for the antioxidative and antigenotoxic activity in EP fraction, the strong activity of an oxygen radical-scavenging enzyme, peroxidase was detected, and the purified horseradish peroxidase also caused the similar antioxidative and antigenotoxic activities. The significance of this finding is discussed from the viewpoint of the preventive role of rice bran against oxygen radical-related chronic diseases.

Antimutagenic Agents↗
PubMed1993

N E. coli, inducible DNA repair is error-prone with regard to lethality.

The umuC gene is a member of the inducible SOS repair network in E. coli. The experiments reported here indicate that the product of the umuC locus can make lethal mistakes during its normal repair function. Such "lethal repair" may be a major factor in establishing a cell's sensitivity to radiation.

Dose-Response Relationship, Radiation↗
PubMed1995

Can an X-ray dose threshold be measured for the induction of SOS repair activity in E. coli.

Survival ("clonogenic ability") and induced DNA repair (SOS repair) have been studied at low X-ray doses in two Escherichia coli strains (GE94 and KY943), both of which contain a recA-lacZ protein fusion. X-ray doses greater than about 0.5 Gray clearly induce SOS repair activity. However, the threshold dose that just activates SOS repair is probably much lower than 0.5 Gray, perhaps as low as 0.001 Gray. It seems unlikely that this dose threshold can be more accurately measured with the recA-lacZ fusion technique.

Dose-Response Relationship, Radiation↗
PubMed1999

The expression of Escherichia coli SOS genes recA and uvrA is inducible by polyamines.

Polyamines are polycationic compounds that have been implicated in a variety of cellular processes. We first report that the expression of recA and uvrA genes in Escherichia coli is inducible by polyamines. The recA and uvrA genes were effectively inducible by spermine (tetra-amine) and less effectively inducible by spermidine (tri-amine). On the other hand, both genes were not significantly inducible by putrescine (diamine) and divalent cation Mg(2+). The expression of both genes was dependent on the charge of the polyamine in the order of spermine (+4), spermidine (+3), and putrescine (+2). The induction of recA and uvrA genes by polyamines showed a dose-dependent relationship and no synergistic effects. Introduction of gyrA mutation conferring DNA relaxation increased the basal expression of recA gene about 2.5-fold compared to the wild type, but did not significantly affect the polyamine-dependent induction ratios of the recA gene. The basal and the polyamine-dependent expression of uvrA gene are not dependent on gyrA mutation. These results suggest that the polyamine-dependent expression of recA and uvrA genes may be regulated in a different way. Our results indicated that polyamines are involved in the SOS induction of recA and uvrA genes at transcriptional levels in E. coli.

Adenosine Triphosphatases↗
PubMed2001

Reduced activity of bamhi variants c54i, c64w, and c54d/c64r is consistent with the substrate-assisted catalysis model.

Three specific mutants, C54I, C54W, and a double-mutant C54D:C64R of restriction endonuclease BamHI, were generated and studied to investigate the role, if any, of the 54th and 64th cysteine residues in the catalysis of BamHI. The mutation was achieved using the megaprimer approach for PCR. The mutant genes were cloned and characterized by sequencing. The mutant and the wild-type proteins were expressed and purified and their kinetic parameters were determined using short synthetic oligonucleotides as substrates. All mutants had higher K(m) values than that of the wild-type enzyme suggesting a decrease in the affinity of the enzyme for its substrate. The mutant protein C54W showed significant changes in the CD spectra vis-a-vis wild-type enzyme and had the lowest K(m)/K(cat) value among the mutants indicative of changes in the secondary structure of the protein. The melting curves of the mutant proteins overlapped that of the wild-type enzyme. Analysis of the K(cat) values in the context of cocrystal structure suggests that the effect of Cys54 mutation is probably through the perturbation of the local structure whereas reduced activity of the double mutant is consistent with the substrate-assisted catalysis mechanism.

Amino Acid Substitution↗
PubMed1993

Plasmid addiction genes of bacteriophage P1: doc, which causes cell death on curing of prophage, and phd, which prevents host death when prophage is retained.

P1 lysogens of Escherichia coli carry the prophage as a stable low copy number plasmid. The frequency with which viable cells cured of prophage are produced is about 10(-5) per cell per generation. Here we show that a significant part of this remarkable stability can be attributed to a plasmid-encoded mechanism that causes death of cells that have lost P1. In other words, the lysogenic cells appear to be addicted to the presence of the prophage. The plasmid withdrawal response depends on a gene named doc (death on curing), encoding a 126 amino acid protein. Expression of doc is not SOS-inducing and killing by Doc is recA-independent. In cells that retain P1 the killing is prevented by the product of a gene named phd (prevent host death), encoding a 73 amino acid protein. The genes phd and doc have been cloned and expressed from a 0.7 kb segment of P1 DNA. The two genes constitute an operon and the synthesis of Doc appears to be translationally coupled to that of Phd. Homologs of the P1 addiction genes are found elsewhere, but phd and doc are unrelated to previously described genes of other plasmids that also cause an apparent increase in plasmid stability by post-segregational killing.

Amino Acid Sequence↗
PubMed1994

Induction of the SOS response by IS1 transposase.

We find that IS1 transposase, like that of Tn10, can induce the SOS response when produced at high levels. Most of the activity (> 80%) requires IS1 ends in cis to the transposase gene and depends strictly on the presence of RecBCD function. This implies that processing of transposase-induced cleavages is responsible for generating the response. Induction of the SOS response during growth in a rich medium is seen only when cells approach stationary phase. The end-dependent induction is abolished by mutations in the ends of IS1 that eliminate transposition activity. IS1 ends in identical orientation on the same plasmid are inactive in transposition but stimulate SOS strongly. Even plasmids with a single end can stimulate SOS, probably as a consequence of plasmid dimer formation which places the ends in direct repeat orientation. These results imply that transposase-induced cleavages do not need inversely oriented ends. The system can therefore be used to dissociate cleavage activity from the other reactions of transposition. Induction of SOS by a series of short (67 to 114 bp) IS1-like elements was found to occur in a cyclical pattern as a function of length with a period of 10 to 11 bp. The frequency of cointegration promoted by these elements showed the same helix-phase dependence. These results suggest that transposase molecules bound to the ends of IS1 interact, and that this interaction is needed for the cleavages that initiate transposition.

Base Sequence↗
PubMed1999

SOS mutagenesis results from up-regulation of translesion synthesis.

Irradiation of DNA with ultraviolet light generates a variety of photolesions. Among them, are cyclobutane pyrimidine dimers (CPD) and (6-4) photoproducts blocking lesions that interfere with DNA replication if left unrepaired. In addition to efficient pre-replicative excision repair mechanisms, cells have evolved damage tolerance pathways enabling them to replicate lesion-containing DNA molecules either by directly replicating through the damaged base (translesion synthesis, TLS) or by employing the locally undamaged complementary strand thus avoiding the lesion (damage avoidance pathways, DA). Using double-stranded vectors with a single T(6-4)T UV lesion and a strand segregation analysis (SSA), we have measured the relative utilization of the two tolerance pathways (TLS and DA) in Escherichia coli. During the SOS response the error-prone TLS pathway is strongly stimulated ( approximately 20-fold) at the expense of the error-free DA pathways. Thus, up-regulation of TLS may turn out to be a general property of the SOS response; a similar conclusion was previously reached with the frameshift-inducing N-2-acetylaminofluorene adduct. Therefore, as far as its contribution to damaged DNA replication is concerned, the SOS response appears to be an induced mutator state rather than a survival strategy. Depending on the base inserted opposite the lesion, TLS can be error-free or mutagenic. In a wild-type strain, both forms of TLS are increased to a similar extent during the SOS response. In contrast, in a DeltaumuDC strain induction of TLS is totally abolished, demonstrating that the UmuDC proteins usually thought to be specifically involved in mutagenesis facilitate the recovery of both error-free and mutagenic replication intermediates in vivo.

DNA↗
PubMed2000

A comparative study of global stress gene regulation in response to overexpression of recombinant proteins in Escherichia coli.

Global gene regulation throughout the Escherichia coli stress response to overexpression of each of five recombinant proteins was evaluated. Reverse-transcriptase polymerase chain reaction-amplified mRNA from induced and control cells were hybridized with a DNA array of Kohara clones representing 16% (700 genes) of the E. coli genome. Subsequently, Northern analysis was performed for quantification of specific gene dynamics and statistically significant overlap in the regulation of 11 stress-related genes was found using correlation analysis. The results reported here establish that there are dramatic changes in the transcription rates of a broad range of stress genes (representing multiple regulons) after induction of recombinant protein. Specifically, the responses included significantly increased upregulation of heat shock (ftsH, clpP, lon, ompT, degP, groEL, aceA, ibpA), SOS/DNA damage (recA, lon, IS5 transposase), stationary phase (rpoS, aceA), and bacteriophage life cycle (ftsH, recA) genes. Importantly, similarities at the microscopic (gene) level were not clearly reflected at the macroscopic (growth rate, lysis) level. The use of such dynamic data is critical to the design of gene-based sensors, the engineering of metabolic pathways, and the determination of parameters (harvest and induction times) needed for successful recombinant E. coli fermentations.

Bacteriophage lambda↗
PubMed1997

Genotoxicity of acyl glucuronide metabolites formed from clofibric acid and gemfibrozil: a novel role for phase-II-mediated bioactivation in the hepatocarcinogenicity of the parent aglycones?

Glucuronides formed from carboxylate-containing xenobiotics are more chemically reactive than most Phase II conjugates. However, while they have been shown to form protein adducts, their reactions with DNA have received little attention. We thus used the M13 forward mutational assay to assess the genotoxicity of acyl glucuronides formed from two widely used fibrate hypolipidemics, clofibric acid and gemfibrozil. Single-stranded M13mp19 bacteriophage DNA was incubated in pH 7.4 buffer for 16 h in the presence of 0, 1, 2.5, and 5 mM concentrations of each glucuronide as well as the respective aglycones. The modified DNA was then transfected into SOS-induced competent Escherichia coli JM105 cells and the transfection efficiency was determined after phage growth overnight at 37 degrees C. Significantly, both acyl glucuronides, but not the aglycones, caused a concentration-dependent decrease in the transfection efficiency of the DNA, with a greater than 80% decrease in phage survival produced by the 5 mM concentrations of the glucuronides. No increase in lacZa mutations accompanied the loss of phage survival. We propose that these genotoxic effects involve reactions with nucleophilic centers in DNA via a Schiff base mechanism that is analogous to the glycosylation of DNA by endogenous sugars. Since strand nicking is known to accompany such damage, we also analyzed glucuronide-treated pSP189 plasmids for strand breakages via agarose gel electrophoresis. Both clofibric acid and gemfibrozil glucuronides produced significant concentration-related strand nicking and exhibited over 10-fold greater reactivity than the endogenous glycosylating agent, glucose 6-phosphate. On the basis of these findings, the possibility that this novel bioactivation route participates in the carcinogenicity of the fibrate hypolipidemics deserves investigation.

Clofibric Acid↗
PubMed1996

Defining the SOS operon of coliphage 186.

We have sequenced the LexA-controlled operon of coliphage 186 that carries the tum gene, whose product is necessary for UV induction of the 186 prophage. The operon consists of orf95 and orf97, and we have identified orf95 as the tum gene. The major translation products from orf95 result from internal initiations and modulate Tum activity. Tum is the product of the full-length Orf95 protein. The second gene of the operon, orf97, is of unknown function but, while it has little effect on prophage induction, its presence in the cell totally blocks infection of that cell by 186.

Amino Acid Sequence↗
PubMed2004

Stress induced by recombinant protein production in Escherichia coli.

Strong production of recombinant proteins interferes with cellular processes in many ways. Drainage of precursors and energy urges the cell to readjust metabolic fluxes and enzyme composition, stress responses are induced, and hence the cellular activity is shifted from growth to reorganisation of biomass. This may result in inhibition of growth or low level of product accumulation. The extent of the bacterial stress response is determined by the specific properties of the recombinant protein, and by the rates of transcription and translation. Taking into account the capacities of the host for protein processing and physiological adaptation, production schemes can be developed that enhance volumetric productivity and sustainability of the process.

Adaptation, Physiological↗
PubMed1993

Induction of SOS like responses by nitrofurantoin in Vibrio cholerae el tor cells.

Treatment of Vibrio cholerae el tor strain SLH22(J) with nitrofurantoin induced dose-dependent prophage 'kappa', the maximum induction being 6-fold the spontaneous induction level. UV-inactivated 'kappa' phages were Weigle reactivated, the maximum Weigle factor being 1.8 and 2.0 respectively in nitrofurantoin and UV pretreated el tor strain H218 Smr. Nitrofurantoin treatment also caused significant filamentation of the el tor strain H218 Smr and mutation of these cells from ampicillin sensitivity to ampicillin resistance. The levels of the four SOS-like responses induced by this drug were low but significant.

Bacteriophages↗
PubMed1991

Molecular analysis of the Bacillus subtilis recF function.

recF resides between the dnaN and gyrB genes of Bacillus subtilis. The recF15 mutation results in replacement of a glutamate residue in the wild type with a lysine residue in the mutant RecF protein. We investigated the in vivo regulation of recF using a transcriptional fusion to the xylE gene and assaying mRNA production. We found that novobiocin leads to a four-fold induction in recF gene expression, but this is not observed in a gyrB mutant strain. Enhancement of expression of the recF gene in the presence of novobiocin is unrelated to the SOS response. The RecF protein, which has a predicted molecular mass of 42.2 kDa, does not seem to be involved in its own regulation.

Bacillus subtilis↗