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1.
Cytotoxic 1-methyladenine (1-meA) and 3-methylcytosine (3-meC) lesions induced in DNA and RNA in vitro and in pre-damaged DNA and RNA bacteriophages in vivo are repaired by the Escherichia coli (E. coli) protein AlkB and a human homolog, ALKBH3. However, it is not known whether endogenous RNA is repaired in vivo by repair proteins present at physiological concentrations. The concept of RNA repair as a biologically relevant process has therefore remained elusive. Here, we demonstrate AlkB-mediated repair of endogenous RNA in vivo by measuring differences in lesion-accumulation in two independent AlkB-proficient and deficient E. coli strains during exposure to methyl methanesulfonate (MMS). Repair was observed both in AlkB-overproducing strains and in the wild-type strains after AlkB induction. RNA repair appeared to be highest in RNA species below 200 nucleotides in size, mainly comprising tRNAs. Strikingly, at least 10-fold more lesions were repaired in RNA than in DNA. This may be a consequence of some 30-fold higher levels of aberrant methylation in RNA than in DNA after exposure to MMS. A high primary kinetic isotope effect (>10) was measured using a deuterated methylated RNA substrate, D3-1me(rA), demonstrating that it is the catalytic step, and not the search step that is rate-limiting. Our results demonstrate that RNA repair by AlkB takes place in endogenous RNA as part of an adaptive response in wild-type E. coli cells. 相似文献
2.
《Mutation Research Letters》1993,301(2):125-134
The cytotoxic and mutagenic effects of 4-hydroxyaminobiphenyl (N-OH-ABP) were studied using Escherichia coli strains with different repair capacities. N-OH-ABP was equally cytotoxic for uvrA and recA mutants as well as in wild-type cells while polA mutants strains proved particularly sensitive to its toxicity. In contrast, the mutation frequency in the uvrA strains tested was elevated to 30–400-fold the wild-type values. We suggest that aminobiphenyl-DNA adducts responsible for mutation are repaired by UVR endonuclease but different pathways exist for removal of DNA lesions responsible for bacterial killing. From the 32P-postlabelling analysis, it was concluded that ABP-DNA adducts can be relatively rapidly repaired in wild-type strains, while persisting in the uvrA strains. 相似文献
3.
Various E. coli mutants, deficient in DNA repair, differed in their response to increasing concentrations of N-nitroso-N-methylurea (NMU).Loss of viability due to exposure to NMU was greatest in those strains with a reduced capacity for repair of single-strand breaks. Viability of wild-type and uvrA? strains was not affected by NMU concentrations up to 3.0 mM. Some loss of viability occurred, at the higher NMU concentrations, in both strains carrying exrA? while strains carrying uvrA?polA? or recA? were the most sensitive. The results support the hypothesis that the lethal effect of NMU on repair-deficient E. coli was due to its ability to induce single-strand breaks.Induction of mutations by NMU was observed in all the strains used and the results suggested that NMU damage per se was the major mutational event. The dose response curve for induction of revertants by NMU was, however, influenced by the repair system(s) present. The number of revertants scored at the higher NMU concentrations was greater in those strains lacking the recA and polA dependent repair functions than in the wild-type strain. However, at NMU concentrations below 2.0 mM the numbers of revertants induced in exrA? carrying strains, prossessing accurate rec-dependent repair, were lower than the comparable wild-type values. The evidence suggests that the uvrA gene product also acts on some, possibly non-mutagenic, types of NMU damage and that error-prone repair of these lesions increases the number of potential revertants. 相似文献
4.
《Mutation Research/DNA Repair Reports》1983,112(5):275-286
A series of Escherichia coli strains deficients in single-stranded DNA-binding protein (SSB) and DNA polymerase I was constructed in order to analyze the effects of these mutations on DNA repair resynthesis after UV-irradiation. Since SSB has been suggested to play a role in protecting single-stranded regions which may transiently exist during excision repair and since long single-stranded regions are believed to occur frequently as repair intermediates in strains deficient in DNA polymerase I, studies of repair resynthesis and strand rejoining were performed on strains containing both the ssb-1 and polA1 mutations. Repair resynthesis appears to be slightly decreased in the ssb-1 strain at 42°C relative to the wild-type; however, this effect is not enhanced in a polA1 derivative of this strain. After UV-irradiation, the single-strand molecular weight of the DNA of an ssb-1 strain decreases and fails to recover to normal size. These results are discussed in the context of long patch repair as an inducible component of repair resynthesis and of the protection of intermediates in the excision repair process by SSB. A direct role for SSB in repair resynthesis involving modulation of the proteins involved in this mode of DNA synthesis (particularly stimulation of DNA polymerase II) is not supported by our findings. 相似文献
5.
Liqiu Ma Yusuke Kazama Hirokazu Inoue Tomoko Abe Shin Hatakeyama Shuuitsu Tanaka 《Fungal biology》2013,117(4):227-238
Heavy-ion beams are known to cause great damage to cellular components and are particularly renowned for their ability to generate DNA double-strand breaks (DSBs). To gain insight into the mutagenic effect of carbon-ion beams and how such damage is repaired by the cell, Neurospora crassa mutants deficient in one of three components involved in the repair of DSBs, nonhomologous end-joining (NHEJ), homologous recombination repair (HR), and the Mre11-Rad50-Xrs2 (MRX) complex, were irradiated with a carbon-ion beam and killing effect, mutation frequencies, and the type of mutation incurred by survivors were analysed. The sensitivity of the NHEJ-deficient strain (mus-52) was higher than that of the wild-type and the HR-deficient (mei-3) strains at low doses of radiation, but was little changed as the level increased. As a result both the wild-type and HR-deficient strains were more sensitive than the NHEJ-deficient strain at high radiation levels. In addition, the frequency of forward mutation at the adenine-3 (ad-3) loci of the NHEJ-deficient mutant was lower than that of the wild-type strain at all levels, while the mutation frequency of the HR-deficient strain was consistently ∼3-fold higher than the wild-type. From the comparison of mutation type of each strain, deletions were frequently observed in wild-type strain, whilst base substitution and deletion in the mus-52 and mei-3 strains. These mutations resulting from carbon-ion-beam irradiation depend on the mechanism invoked to cope with DSBs. Furthermore, in wild-type cells, these mechanisms likely compete to repair DSBs. 相似文献
6.
We have measured UV-induced mutation frequencies in yeast in a forward, nonselective assay system by scoring white adex ade2 double auxotrophs among parental red-pigmented ade2 clones. The frequencies of sectored and pure mutant clones were determined separately. In excision-defective strains carrying the genes rad1–1, rad3–2 and rad4–4, as well as in the double mutants, rad 1–1 rad 3–2 and rad 1–1 rad 4–4, considerably more sectored than pure clones are induced in the low-dose range; in repair-competent strains, pure mutant clones substantially outnumber the sectored clones. These results can be explained on the basis of known differences in the timing of error-prone repair during the cell division cycle; that is, we assume that error-prone repair occurs primarily before replication in RAD wild-type strains but after replication in excision-deficient mutants. It has been suggested that excision deficiency has a pleiotropic effect on heteroduplex repair and nucleotide excision repair; however, the high percentage (36.6%) of half-sectored clones found in the rad1–1 strain is hard to reconcile with this hypothesis. We propose that heteroduplex repair occurs subsequent to error-prone repair in both excision-proficient and excision-deficient strains. 相似文献
7.
The survival of wild-type and repair-deficient Escherichia coli treated with cis-Pt(NH3)2Cl2, trans-Pt(NH3)2Cl2 and [Pt(dien)Cl]Cl (dien = H2NCH2CH2NHCH2CH2NH2) was inversely correlated with the ability of these compounds to inhibit DNA synthesis in different bacterial strains. The relative amounts of these 3 compounds covalently bound to DNA immediately after treatment with the same dose were, respectively, 1:?2:1, their relative abilities to inhibit DNA synthesis were 6:1:0 and their relative toxicities toward the wild-type and uvrA strains were 3–5:1:0. More repair synthesis, as measured by density-gradient centrifugation techniques, was observed in wild-type bacteria after treatment with the cis than with the trans isomer whereas no repair synthesis was detected after exposure to [Pt(dien)Cl]Cl.These results are consistent with the hypothesis that cis-Pt(NH3)Cl2 binds to DNA and inhibits DNA synthesis thereby killing the cell. The lower toxicity of this compound toward wild-type bacteria compared with repair-deficient strains is in part a consequence of DNA repair. trans-Pt(NH3)2Cl2 and [Pt(dien)Cl]Cl are less toxic than the cis isomer; this lesser toxicity is not a consequence of low levels of DNA binding or enhanced repair of the lesions but appears to reflect a weaker inhibition of DNA synthesis by these Pt-DNA adducts. 相似文献
8.
《Mutation Research/DNA Repair Reports》1987,183(1):21-29
An increased resistance to the toxic and mutagenic activity of the antitumor drug cis-diamminedichloroplatinum(II) (cis-DDP) in the E. coli strain BS21 compared to its wild-type parent, F26, has been reported. This resistance was neither due to different binding of cis-DDP to DNA nor to adaptive DNA repair (Germanier et al., 1984) In the present work, we found that mutation of the uvrA, recA and polA genes did not abolish the resistance of BS21 to the toxic action of cis-DDP. The lower mutability of BS21 was not influenced by the polA mutation, while uvrA greatly reduced and recA eliminated the mutagenic activity of cis-DDP in both strains. Treatment of BS21 and F26 with equal doses of cis-DDP produced the same initial number of platinum-DNA lesions. Little excision repair was detected in vivo in either strain during 6-h post-treatment incubation, the F26 strain being the most efficient of the two for this process. In contrast, F26 and BS21 were transformed identically by pBR322 DNA which had been treated with cis-DDP in vitro. Analysis of the platinum-DNA adducts which were formed between cis-DDP and salmon sperm DNA in the buffer conditions of this experiment suggests that plasmid DNA contains 80% monofunctional adducts and 20% bifunctional bis-guanine adducts.These data indicate that the selective toxicity and mutagenicity of these two strains in vivo are neither a result of different numbers of Pt-DNA lesions nor of their repair. The selectivity disappeared when the two bacterial strains were transformed by pBR322 DNA containing identical platinum-DNA lesions, suggesting that the biochemical events which process platinum-DNA lesions are the same in both strains. Hence, it appears that cis-DDP may form qualitatively different platinum-DNA adducts in the BS21 and F26 strains which are responsible for the different toxicity and mutagenicity. 相似文献
9.
J F Lemontt 《Mutation research》1978,50(1):57-66
The fate of presumed premutational DNA lesions induced by hydrazine was studied under a variety of post-treatment conditions in wild-type and in excision repair-defective (rad2-1) strains of Saccharomyces cerevisiae. In all strains the full extent of hydrazine-induced, forward mutability from CAN1 to can1 (canavanine resistance) was dependent upon post-treatment cell division in mutagen-free synthetic or complex growth medium before plating on canavanine-containing selective agar and could be blocked by inhibitors of DNA synthesis (hydroxyurea) or protein synthesis (cycloheximide) contained in the growth medium. Following the growth-inhibitory period, cells were permitted to grow in fresh medium lacking inhibitors to determine the level of induced mutation remaining. Nearly all induced mutability was lost after a one-day growth inhibition, compared with mutagen-treated control samples subsequently grown twice in medium lacking inhibitor. In the wild type, half the induced mutability was lost after 3 h. The data suggest that premutational DNA lesions induced by hydrazine were removed, or possibly rendered non-mutagenic, by some error-free repair process that acted before mutation fixation by base mispairing during DNA replication. Since rad2-1 and RAD strains both exhibited loss of mutability, this process is not dependent upon the activity of an intact pyrimidine dimer excision-repair system. 相似文献
10.
Folate antagonists, such as aminopterin, methotrexate and various sulfonamides, block de novo thymidylate biosynthesis in Saccharomyces cerevisiae. The resulting starvation for thymine nucleotides is lethal and recombinagenic in RAD wild-type strains. In this paper we report our studies of these effects in repair-deficient yeast. Antifolate treatment of various rad mutants revealed that repair defects influence the killing and recombination caused by thymidylate deprivation. Compared to a RAD wild-type strain, diploids homozygous for rad3, rad6 or rad18 were more resistant to cell killing. Thus, contrary to findings with conventional DNA-damaging agents, the lethal effects of thymidylate starvation appear to be ameliorated by certain DNA repair deficiencies. On the other hand, a rad50 strain was extremely sensitive to the antifolates. Within this series of diploids, increasing sensitivity to thymidylate starvation was accompanied by an increase in recombination frequencies. The degrees of lethality and recombination, induced by thymidylate depletion, were correlated with the severity of DNA-strand breakage in the RAD and rad50 strains. Experiments with diploids homozygous for rad52, rad54 or rad57 suggested that aborted recombination events, provoked by thymidylate deprivation, caused chromosome loss. Furthermore, the repair defects in these mutants indicated that double-strand breaks are among the lethal lesions induced by thymine nucleotide starvation. Finally, we discuss the possibility that the recombinagenicity of thymidylate stress may account for one type of acquired resistance to methotrexate in mammalian cells. 相似文献
11.
Two genes of Aspergillus nidulans are known to function in UV mutagenesis, but have been assigned to different epistasis groups: uvsC, which is also required for meiosis and mitotic recombination, and uvsI, which may have no other function. To clarify their role in error-prone repair and to investigate their interaction, uvsI and uvsC single and uvsI;uvsC double mutant strains were further tested for mutagen sensitivities and characterized for effects on mutation. Spontaneous and induced frequencies were compared in forward and reverse mutation assays. All results confirmed that uvsI and uvsC are members of different epistasis groups, and demonstrated that these uvs mutants have very different defects in UV mutagenesis. The uvsI strains showed wild-type frequencies in all forward mutation tests, but greatly reduced spontaneous and UV-induced reversion of some, but not other, point mutations. In contrast, uvsC had similar effects in all assay systems: namely pronounced mutator effects and greatly reduced UV mutagenesis. Interestingly, the uvsI;uvsC double mutant strains differed from both single mutants; they clearly showed synergism for all types of reversion tested: none were ever obtained spontaneously, nor after induction by UV or EMS (ethylmethane sulfonate). Based on these results, we conclude that uvsI is active in a mutation-specific, specialized error-prone repair process in Aspergillus. In contrast, uvsC, which is now known to show sequence homology to recA, has a basic function in mutagenic UV repair in addition to recombinational repair, similar to recA of Escherichia coli. 相似文献
12.
Adriana Antúnez de Mayolo Ivana Sunjevaric Robert Reid Uffe H. Mortensen Rodney Rothstein Michael Lisby 《DNA Repair》2010,9(1):23-32
Spontaneous mitotic recombination is a potential source of genetic changes such as loss of heterozygosity and chromosome translocations, which may lead to genetic disease. In this study we have used a rad52 hyper-recombination mutant, rad52-Y66A, to investigate the process of spontaneous heteroallelic recombination in the yeast Saccharomyces cerevisiae. We find that spontaneous recombination has different genetic requirements, depending on whether the recombination event occurs between chromosomes or between chromosome and plasmid sequences. The hyper-recombination phenotype of the rad52-Y66A mutation is epistatic with deletion of MRE11, which is required for establishment of DNA damage-induced cohesion. Moreover, single-cell analysis of strains expressing YFP-tagged Rad52-Y66A reveals a close to wild-type frequency of focus formation, but with foci lasting 6 times longer. This result suggests that spontaneous DNA lesions that require recombinational repair occur at the same frequency in wild-type and rad52-Y66A cells, but that the recombination process is slow in rad52-Y66A cells. Taken together, we propose that the slow recombinational DNA repair in the rad52-Y66A mutant leads to a by-pass of the window-of-opportunity for sister chromatid recombination normally promoted by MRE11-dependent damage-induced cohesion thereby causing a shift towards interchromosomal recombination. 相似文献
13.
Milena Sedliaková Viera Slezáriková Jela Brozmanová František Mašek Viktória Bayerová 《Mutation research》1980,71(1):15-23
3 wild-type strains of E. coli, namely K12 AB2497, B/r WP2 and 15 555-7v proficient in excision and post-replication repair, differ markedly in their UV resistance. To elucidate this difference, the influence was investigated of induction by application of inducing fluence (IF) before lethal fluence (LF) on repair processes after LF. In cells distinguished by low UV resistance (E. coli 15 555-7; E. coli B/r WP2), dimer excision was less complete in cultures irradiated with IF + LF than in cultures irradiated with LF only. The highly resistant E. coli K12 AB2497 performed complete excision both after IF + LF or after LF alone. All 3 types of cell survived better after IF + LF than after LF only. Because, in most strains so far investigated, the application of IF reduced dimer excision and increased survival, dimer excision per se does not appear important for survival.We conclude that the rate and completeness of dimer excision can serve as a measure of efficiency of the excision system whose action is necessary for repair of another lesion. Cells of all investigated strains could not resume DNA replication and died progressively when irradiated with LF and post-incubated with chloramphenicol (LF CAP+). Thus, it appears that inducible proteins are necessary for repair in all wild-type E. coli cells give with potentially lethal doses of UV irradiation. 相似文献
14.
Escherichia coli Strains Lacking Protein HU Are UV Sensitive due to a Role for HU in Homologous Recombination
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hupA and hupB encode the α and β subunits of the Escherichia coli histone-like protein HU. Here we show that E. coli hup mutants are sensitive to UV in the rec+ sbc+, recBC sbcA, recBC sbcBC, umuDC, recF, and recD backgrounds. However, hupAB mutations do not enhance the UV sensitivity of resolvase-deficient recG ruvA strains. hupAB uvrA and hupAB recG strains are supersensitive to UV. hup mutations enhance the UV sensitivity of ruvA strains to a much lesser extent but enhance that of rus-1 ruvA strains to the same extent as for rus+ ruv+ strains. Our results suggest that HU plays a role in recombinational DNA repair that is not specifically limited to double-strand break repair or daughter strand gap repair; the lack of HU affects the RecG RusA and RuvABC pathways for Holliday junction processing equally if the two pathways are equally active in recombinational repair; the function of HU is not in the substrate processing step or in the RecFOR-directed synapsis action during recombinational repair. Furthermore, the UV sensitivity of hup mutants cannot be suppressed by overexpression of wild-type or mutant gyrB, which confers novobiocin resistance, or by different concentrations of a gyrase inhibitor that can increase or decrease the supercoiling of chromosomal DNA. 相似文献
15.
Induction of back mutations to prototrophy by methylene blue (MB)-sensitized photodynamic (PD) treatment has been studied in wild-type and repair-deficient strains of Salmonella typhimurium carrying either the base-pair substitution mutation hisG46 or the frameshift mutation hisD3052. We found that reversion of the hisG46 mutation was increased in a strain carrying a uvrB deletion and decreased in a strain carrying a recA-type mutation. Reversion of the hisD3052 (frameshift) mutation, on the other hand, was decreased in both uvrB deletion and recA-type strains. The former results are consistent with the hypothesis that the majority of MB-sensitized PD-induced base-pair substitution mutations arise by a mechanism similar to that currently believed to be involved in UV mutagenesis. The latter results suggest that PD-induced frameshift mutations may arise in some other way, and two possible mechanisms involving sequential action of the excision repair and recombinational repair pathways are considered. 相似文献
16.
Anja Bauermeister Claudia Hahn Petra Rettberg Günther Reitz Ralf Moeller 《Archives of microbiology》2012,194(11):959-966
To study the effects of heat shock on Deinococcus radiodurans and the role of DNA repair in high temperature resistance, different strains of D. radiodurans (wild type, recA, irrE, and pprA) were treated with temperatures ranging from 40 to 100?°C under wet and dry conditions. The mutant strains were more sensitive to wet heat of ≥60?°C and dry heat of ≥80?°C than the wild type. Both wild-type and DNA repair-deficient strains were much more resistant to high temperatures when exposed in the dried state as opposed to cells in suspension. Molecular staining techniques with the wild-type strain revealed that cells in the dried state were able to retain membrane integrity after drying and subsequent heat exposure, while heat-exposed cells in suspension showed significant loss of membrane integrity and respiration activity. The results suggest that the repair of DNA damage (e.g., DNA double-strand breaks by RecA and PprA) is essential after treatment with wet heat at temperatures >60?°C and dry heat >80?°C, and the ability of D. radiodurans to stabilize its plasma membrane during dehydration might represent one aspect in the protection of dried cells from heat-induced membrane damage. 相似文献
17.
Beata Janowska Marek Komisarski Paulina Prorok Beata Soko?owska Jaros?aw Ku?mierek Celina Janion Barbara Tudek 《International journal of biological sciences》2009,5(6):611-620
One of the major products of lipid peroxidation is trans-4-hydroxy-2-nonenal (HNE). HNE forms highly mutagenic and genotoxic adducts to all DNA bases. Using M13 phage lacZ system, we studied the mutagenesis and repair of HNE treated phage DNA in E. coli wild-type or uvrA, recA, and mutL mutants. These studies revealed that: (i) nucleotide excision and recombination, but not mismatch repair, are engaged in repair of HNE adducts when present in phage DNA replicating in E. coli strains; (ii) in the single uvrA mutant, phage survival was drastically decreased while mutation frequency increased, and recombination events constituted 48 % of all mutations; (iii) in the single recA mutant, the survival and mutation frequency of HNE-modified M13 phage was slightly elevated in comparison to that in the wild-type bacteria. The majority of mutations in recA- strain were G:C → T:A transversions, occurring within the sequence which in recA+ strains underwent RecA-mediated recombination, and the entire sequence was deleted; (iv) in the double uvrA recA mutant, phage survival was the same as in the wild-type although the mutation frequency was higher than in the wild-type and recA single mutant, but lower than in the single uvrA mutant. The majority of mutations found in the latter strain were base substitutions, with G:C → A:T transitions prevailing. These transitions could have resulted from high reactivity of HNE with G and C, and induction of SOS-independent mutations. 相似文献
18.
Lorraine J. Gudas 《Journal of molecular biology》1976,104(3):567-587
Certain temperature-sensitive Escherichia coli cell division mutants and DNA repair mutants were treated in several ways to alter DNA synthesis or cell division. The bacteria were pulsed with [35S]methionine; then membrane proteins were prepared and examined using sodium dodecyl sulfate/polyacrylamide slab gels. Autoradiography was performed on the slab gels so that the rate of synthesis of protein X could be determined by microdensitometry.Several changes in the rate of synthesis of the 40,000 molecular weight protein X were found in the different mutants. The wild-type (rec+ and lex+) strains synthesized protein X in response to DNA synthesis inhibition. However, neither recA? strains nor lex? strains synthesized protein X.Both the filament forming, temperature-sensitive mutants tif? and tsl? (which was derived from lex?) synthesized protein X when DNA synthesis was inhibited, but at rates different from the wild-type strains. Moreover, these strains also produced protein X at their non-permissive temperature, even though DNA synthesis was not inhibited. In the tif? mutant, the rate of synthesis of protein X was influenced by the addition of nucleic acid precursors.A double mutant tsl?recA? produced protein X when DNA synthesis was inhibited, or at the non-permissive temperature (although DNA synthesis was normal). This was the only strain carrying a recA? mutation capable of synthesizing protein X.From these results it is suggested that the genes lex, recA and tif comprise a system that controls DNA repair and limits DNA degradation by the recBC nuclease. The inducer of this control system might be a DNA degradation product. 相似文献
19.
Nuclease Activity of Saccharomyces cerevisiae Mre11 Functions in Targeted Nucleotide Alteration
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Oligonucleotides can be used to direct site-specific changes in genomic DNA through a process in which mismatched base pairs in the oligonucleotide and the target DNA are created. The mechanism by which these complexes are developed and resolved is being studied by using Saccharomyces cerevisiae as a model system. Genetic analyses have revealed that in all likelihood the reaction occurs in two phases: DNA pairing and DNA repair. While the former phase involves strand assimilation, the latter phase likely involves an endonucleolytic processing step that leads to joint resolution. In this study, we established the importance of a functioning MRE11 gene in the overall reaction, as yeast strains deficient in MRE11 exhibited severely reduced activity. The activity could be rescued by complementation with wild-type MRE11 genes but not with MRE11 alleles lacking the nuclease function. Taken together, the data suggest that Mre11 provides nuclease activity for targeted nucleotide exchange, a process that could be used to reengineer yeast genes. 相似文献
20.
《Mutation Research/DNA Repair Reports》1987,183(2):129-137
Plasmid pBR322 was modified in vitro with the antitumor compound cis-diamminedichloroplatimum(II) (cis-DDP) or the isomeric trans-DDP. The numbers of platinum adducts were determined by atomic absorption spectrophotetry. DNA-repair-proficient and various DNA-repair-deficient (uvrB, uvrD, recB and recA) strains of Escherichia coli were transformed by the damaged plasmids and the ratios of the transformation frequencies of cells by damaged plasmids relative to those by untreated plasmids were determined. Results of transformation assays indicated that the uvrB gene function was essential for repair of plasmid DNA damaged with cis-DDP. A functional recA gene product seemed to be of minor importance for repair of plasmids damaged with cis-DDP. trans-DDP had a different effect on plasmid DNA. trans-DDP-modified DNA was better able to transform cells than cis-DDP-modified DNA, and the DNAs appeared to be repaired differently. Prior induction of SOS functions increased the survival of plasmids treated with cis-DDP in wild-type and uvrD mutants, but did not increase the survival of plasmids damaged with trans-DDP in these strains. In in vitro repair experiments, plasmid DNA modified with cis-DDP was more readily incised by the UVRABC excinuclease than that modified with trans-DDP. 相似文献