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1.
Intrachromosomal recombination between repeated elements can result in deletion (DEL recombination) events. We investigated the inducibility of such intrachromosomal recombination events at different stages of the cell cycle and the nature of the primary DNA lesions capable of initiating these events. Two genetic systems were constructed in Saccharomyces cerevisiae that select for DEL recombination events between duplicated alleles of CDC28 and TUB2. We determined effects of double-strand breaks (DSBs) and single-strand breaks (SSBs) between the duplicated alleles on DEL recombination when induced in dividing cells or cells arrested in G1 or G2. Site-specific DSBs and SSBs were produced by overexpression of the I-Sce I endonuclease and the gene II protein (gIIp), respectively. I-Sce I-induced DSBs caused an increase in DEL recombination frequencies in both dividing and cell-cycle-arrested cells, indicating that G1- and G2-arrested cells are capable of completing DSB repair. In contrast, gIIp-induced SSBs caused an increase in DEL recombination frequency only in dividing cells. To further examine these phenomena we used both gamma-irradiation, inducing DSBs as its most relevant lesion, and UV, inducing other forms of DNA damage. UV irradiation did not increase DEL recombination frequencies in G1 or G2, whereas gamma-rays increased DEL recombination frequencies in both phases. Both forms of radiation, however, induced DEL recombination in dividing cells. The results suggest that DSBs but not SSBs induce DEL recombination, probably via the single-strand annealing pathway. Further, DSBs in dividing cells may result from the replication of a UV or SSB-damaged template. Alternatively, UV induced events may occur by replication slippage after DNA polymerase pausing in front of the damage. 相似文献
2.
A genetic system selecting for deletion events (DEL recombination) due to intrachromosomal recombination has previously been constructed in the yeastSaccharomyces cerevisiae. Intrachromosomal recombination is inducible by chemical and physical carcinogens. We wanted to understand better the mechanism of induced DEL recombination and to attempt to determine in which phase of the cell cycle DEL recombination is inducible. Yeast cells were arrested at specific phases of the cell cycle, irradiated with UV or γ-rays, and assayed for DEL recombination and interchromosomal recombination. In addition, the contribution of intrachromatid crossing-over to the number of radiation induced DEL recombination events was directly investigated at different phases of the cell cycle. UV irradiation induced DEL recombination preferentially in S phase, while γ-rays induced DEL recombination in every phase of the cell cycle including G1. UV and γ-radiation induced intrachromatid crossing over preferentially in G1, but it accounted at the most for only 14% of the induced DEL recombination events. The possibility is discussed that single-strand annealing or one-sided invasion events, which can occur in G1 and may be induced by a double-strand break intermediate, may be responsible for a large proportion of the induced DEL recombination events. 相似文献
3.
A genetic system selecting for deletion events (DEL recombination) due to intrachromosomal recombination has previously been constructed in the yeastSaccharomyces cerevisiae. Intrachromosomal recombination is inducible by chemical and physical carcinogens. We wanted to understand better the mechanism of induced DEL recombination and to attempt to determine in which phase of the cell cycle DEL recombination is inducible. Yeast cells were arrested at specific phases of the cell cycle, irradiated with UV or -rays, and assayed for DEL recombination and interchromosomal recombination. In addition, the contribution of intrachromatid crossing-over to the number of radiation induced DEL recombination events was directly investigated at different phases of the cell cycle. UV irradiation induced DEL recombination preferentially in S phase, while -rays induced DEL recombination in every phase of the cell cycle including G1. UV and -radiation induced intrachromatid crossing over preferentially in G1, but it accounted at the most for only 14% of the induced DEL recombination events. The possibility is discussed that single-strand annealing or one-sided invasion events, which can occur in G1 and may be induced by a double-strand break intermediate, may be responsible for a large proportion of the induced DEL recombination events. 相似文献
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The srs2 suppressor of UV sensitivity acts specifically on the RAD5- and MMS2-dependent branch of the RAD6 pathway 总被引:1,自引:0,他引:1
Ulrich HD 《Nucleic acids research》2001,29(17):3487-3494
7.
J P O'Neill 《Mutation research》1982,106(1):113-122
The induction of mutations by the alkylating agent ethyl methanesulfonate (EMS) was determined with Chinese hamster ovary cells maintained in serum-free medium to arrest DNA synthesis and cell division. The arrested cultures were treated with EMS and maintained in serum-free medium for various time intervals post-treatment before serum containing medium was added to initiate DNA synthesis and cell division. The concentration-dependent increase in 6-thioguanine-resistant mutants in the arrested cultures was similar to that found with exponentially dividing cultures when serum was added to the arrested cultures immediately after the EMS treatment; the time course of phenotypic expression was also similar with both cultures. In addition, maintenance of the arrested cultures in serum-free medium for up to 18 days post-treatment resulted in no change in the mutant frequency. This suggests that the mutagenic damage is not removed in these arrested cultures. Furthermore, maintenance of the arrested state for increasing time intervals before serum addition results in decreases in the time necessary for maximum phenotypic expression. Cultures maintained in serum-free medium for 16 days after mutation treatment show complete expression of the mutations with no need for subculture. This last result suggests that the mutagenic damage induced by EMS in Chinese hamster ovary cells is not removed and that this damage results in both the induction and expression of mutation in the absence of DNA replication. 相似文献
8.
The G2/M DNA damage checkpoint inhibits mitosis through Tyr15 phosphorylation of p34cdc2 in Aspergillus nidulans. 总被引:3,自引:2,他引:1
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It is possible to cause G2 arrest in Aspergillus nidulans by inactivating either p34cdc2 or NIMA. We therefore investigated the negative control of these two mitosis-promoting kinases after DNA damage. DNA damage caused rapid Tyr15 phosphorylation of p34cdc2 and transient cell cycle arrest but had little effect on the activity of NIMA. Dividing cells deficient in Tyr15 phosphorylation of p34cdc2 were sensitive to both MMS and UV irradiation and entered lethal premature mitosis with damaged DNA. However, non-dividing quiescent conidiospores of the Tyr15 mutant strain were not sensitive to DNA damage. The UV and MMS sensitivity of cells unable to tyrosine phosphorylate p34cdc2 is therefore caused by defects in DNA damage checkpoint regulation over mitosis. Both the nimA5 and nimT23 temperature-sensitive mutations cause an arrest in G2 at 42 degrees C. Addition of MMS to nimT23 G2-arrested cells caused a marked delay in their entry into mitosis upon downshift to 32 degrees C and this delay was correlated with a long delay in the dephosphorylation and activation of p34cdc2. Addition of MMS to nimA5 G2-arrested cells caused inactivation of the H1 kinase activity of p34cdc2 due to an increase in its Tyr15 phosphorylation level and delayed entry into mitosis upon return to 32 degrees C. However, if Tyr15 phosphorylation of p34cdc2 was prevented then its H1 kinase activity was not inactivated upon MMS addition to nimA5 G2-arrested cells and they rapidly progressed into a lethal mitosis upon release to 32 degrees C. Thus, Tyr15 phosphorylation of p34cdc2 in G2 arrests initiation of mitosis after DNA damage in A. nidulans. 相似文献
9.
Farid E. Ahmed 《Radiation and environmental biophysics》1980,18(1):57-64
Summary Excision repair was studied in normal human and ataxia telangiectasia (AT) cells proficient in repair of UV and its mimetic chemicals, and in xeroderma pigmentosum group C (XP C) cells (deficient in repair of UV and its mimetics), after treatment with several combinations of chemical carcinogens, by the photolysis of bromodeoxyuridine incorporated into parental DNA during repair. Results indicate that repair was additive in AT, and XP C cells treated with N-acetoxy-2-acetylaminofluorene (AAAF) plus ethyl methanesulfonate (EMS) or methyl methanesulfonate (MMS) indicating that there are different rate limiting steps for removal of both types of damage. Data on the combinations of 4-nitroquinoline 1-oxide (4NQO) plus MMS or EMS are difficult to interpret, but they do not indicate inhibition of DNA repair.Research carried out under the auspices of the U.S. Dept. of Energy 相似文献
10.
The novel DNA damage checkpoint protein ddc1p is phosphorylated periodically during the cell cycle and in response to DNA damage in budding yeast. 总被引:25,自引:4,他引:21
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M P Longhese V Paciotti R Fraschini R Zaccarini P Plevani G Lucchini 《The EMBO journal》1997,16(17):5216-5226
The DDC1 gene was identified, together with MEC3 and other checkpoint genes, during a screening for mutations causing synthetic lethality when combined with a conditional allele altering DNA primase. Deletion of DDC1 causes sensitivity to UV radiation, methyl methanesulfonate (MMS) and hydroxyurea (HU). ddc1Delta mutants are defective in delaying G1-S and G2-M transition and in slowing down the rate of DNA synthesis when DNA is damaged during G1, G2 or S phase, respectively. Therefore, DDC1 is involved in all the known DNA damage checkpoints. Conversely, Ddc1p is not required for delaying entry into mitosis when DNA synthesis is inhibited. ddc1 and mec3 mutants belong to the same epistasis group, and DDC1 overexpression can partially suppress MMS and HU sensitivity of mec3Delta strains, as well as their checkpoint defects. Moreover, Ddc1p is phosphorylated periodically during a normal cell cycle and becomes hyperphosphorylated in response to DNA damage. Both phosphorylation events are at least partially dependent on a functional MEC3 gene. 相似文献
11.
The frequency of simian papovirus 40 (SV40) induced transformation of human cells was enhanced after pretreatment with either napthylamine-2,N-methyl-N'-nitrosoguanidine (MNNG), N-acetyl-2-fluorenylacetamide (N-Ac-AAF), benzo[a]pyrene (BP), aflatoxin B1, propane sultone (PS), beta-propiolactone, 4-nitroquinoline oxide (4-NQO), methylmethane sulfonate (MMS) or diethyl nitrosamine (DEN). Posttreatment with 4-NQO, MMS, MNNG or DEN inhibited transformation; while posttreatment with either aflatoxin B1, beta-propiolactone or napthylamine-2 did not alter transformation similar to the action of N-Ac-AAF and BP. All carcinogens that altered transformation after pretreatment damaged cellular DNA. Pretreatment or posttreatment with carcinogens 3-methylcholanthrene (3-MCA) or 7,12-dimethylbenzanthrene (7,12-DMBA), that did not damage cellular DNA also did not enhance transformation. Moreover, pre- or posttreatment with other weak or non-carcinogens that did not damage cellular DNA did not alter virus induced transformation. All foci formed in the co-carcinogen treated cultures whether the carcinogen inhibited or enhanced transformation were virus directed. While a similar pattern of response existed for carcinogens that either enhance or inhibit transformation, each of the carcinogens that enhanced or inhibited foci formation damaged cellular DNA. Moreover, those carcinogens that enhanced focus formation, compared to the carcinogens that inhibited focus formation, exhibited similar DNA damage profiles. 相似文献
12.
Daigaku Y Mashiko S Mishiba K Yamamura S Ui A Enomoto T Yamamoto K 《Mutation research》2006,600(1-2):177-183
A CAN1/can1Δ heterozygous allele that determines loss of heterozygosity (LOH) was used to study recombination in Saccharomyces cerevisiae cells exposed to ultraviolet (UV) light at different points in the cell cycle. With this allele, recombination events can be detected as canavanine-resistant mutations after exposure of cells to UV radiation, since a significant fraction of LOH events appear to arise from recombination between homologous chromosomes. The radiation caused a higher level of LOH in cells that were in the S phase of the cell cycle relative to either cells at other points in the cell cycle or unsynchronized cells. In contrast, the inactivation of nucleotide excision repair abolished the cell cycle-specific induction by UV of LOH. We hypothesize that DNA lesions, if not repaired, were converted into double-strand breaks during stalled replication and these breaks could be repaired through recombination using a non-sister chromatid and probably also the sister chromatid. We argue that LOH may be an outcome used by yeast cells to recover from stalled replication at a lesion. 相似文献
13.
The 70 kDa subunit of replication protein A is required for the G1/S and intra-S DNA damage checkpoints in budding yeast. 总被引:11,自引:1,他引:10
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The rfa1-M2 and rfa1-M4 Saccharomyces cerevisiae mutants, which are altered in the 70 kDa subunit of replication protein A (RPA) and sensitive to UV and methyl methane sulfonate (MMS), have been analyzed for possible checkpoint defects. The G1/S and intra-S DNA damage checkpoints are defective in the rfa1-M2 mutant, since rfa1-M2 cells fail to properly delay cell cycle progression in response to UV irradiation in G1 and MMS treatment during S phase. Conversely, the G2/M DNA damage checkpoint and the S/M checkpoint are proficient in rfa1-M2 cells and all the checkpoints tested are functional in the rfa1-M4 mutant. Preventing S phase entry by alpha-factor treatment after UV irradiation in G1 does not change rfa1-M4 cell lethality, while it allows partial recovery of rfa1-M2 cell viability. Therefore, the hypersensitivity to UV and MMS treatments observed in the rfa1-M4 mutant might only be due to impairment of RPA function in DNA repair, while the rfa1-M2 mutation seems to affect both the DNA repair and checkpoint functions of Rpa70. 相似文献
14.
Antimutagenic effects of cinnamaldehyde on mutagenesis by chemical agents were investigated in Escherichia coli WP2 uvrA- trpE-. Cinnamaldehyde, when added to agar medium, greatly reduced the number of Trp+ revertants induced by 4-nitroquinoline 1-oxide (4-NQO) without any decrease of cell viability. This antimutagenic effect could not be explained by inactivation of 4-NQO caused by direct interaction with cinnamaldehyde. Mutagenesis by furylfuramide (AF-2) was also suppressed significantly. Mutations induced by methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) were slightly inhibited. However, cinnamaldehyde was not at all effective on the mutagenesis of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Two derivatives of cinnamaldehyde, cinnamyl alcohol and trans-cinnamic acid, did not have as strong antimutagenic effects on 4-NQO mutagenesis as cinnamaldehyde had. Because cinnamaldehyde showed marked antimutagenic effects against mutations induced by UV-mimic mutagens but not those induced by MNNG or EMS, it seems that cinnamaldehyde might act by interfering with an inducible error-prone DNA repair pathway. 相似文献
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16.
The yeast DEL assay measures the frequency of intrachromosomal recombination between two partially-deleted his3 alleles on chromosome XV. The his3Delta alleles share approximately 400bp of overlapping homology, and are separated by an intervening LEU2 sequence. Homologous recombination between the his3Delta alleles results in deletion of the intervening LEU2 sequence (DEL), and reversion to histidine prototrophy. In this study we have attempted to further extend the use of the yeast DEL assay to measure the frequency of chromosome XV gain events. Reversion to His(+)Leu(+) in the haploid yeast DEL tester strain RSY6 occurs upon non-disjunction of chromosome XV sister chromatids, coupled with a subsequent DEL event. Here we have tested the ability of the yeast DEL assay to accurately predict the aneugenic potential of the diversely-acting, known or suspected aneugens actinomycin D, benomyl, chloral hydrate, ethyl methanesulfonate (EMS), methyl methanesulfonate (MMS), and methotrexate. Actinomycin D and benomyl strongly induced aneuploidy. EMS and methotrexate modestly induced aneuploidy, while chloral hydrate and MMS failed to illicit any significant induction. In addition, by FACS-analysis of DNA content it was shown that the majority of both spontaneous- and chemically-induced His(+)Leu(+) revertants were heterodiploid. Thus, our results indicate endoreduplication of almost entire chromosome sets as a major mechanism of aneuploidy induction in haploid Saccharomyces cerevisiae. 相似文献
17.
Elevated mitotic recombination and cell cycle delays are two of the cellular responses to UV-induced DNA damage. Cell cycle delays in response to DNA damage are mediated via checkpoint proteins. Two distinct DNA damage checkpoints have been characterized in Schizosaccharomyces pombe: an intra-S-phase checkpoint slows replication and a G(2)/M checkpoint stops cells passing from G(2) into mitosis. In this study we have sought to determine whether UV damage-induced mitotic intrachromosomal recombination relies on damage-induced cell cycle delays. The spontaneous and UV-induced recombination phenotypes were determined for checkpoint mutants lacking the intra-S and/or the G(2)/M checkpoint. Spontaneous mitotic recombinants are thought to arise due to endogenous DNA damage and/or intrinsic stalling of replication forks. Cells lacking only the intra-S checkpoint exhibited no UV-induced increase in the frequency of recombinants above spontaneous levels. Mutants lacking the G(2)/M checkpoint exhibited a novel phenotype; following UV irradiation the recombinant frequency fell below the frequency of spontaneous recombinants. This implies that, as well as UV-induced recombinants, spontaneous recombinants are also lost in G(2)/M mutants after UV irradiation. Therefore, as well as lack of time for DNA repair, loss of spontaneous and damage-induced recombinants also contributes to cell death in UV-irradiated G(2)/M checkpoint mutants. 相似文献
18.
Homologous recombination and nonhomologous end joining (NHEJ) are important DNA double-strand break repair pathways in many organisms. C. elegans strains harboring mutations in the cku-70, cku-80, or lig-4 NHEJ genes displayed multiple developmental abnormalities in response to radiation-induced DNA damage in noncycling somatic cells. These phenotypes did not result from S-phase, DNA damage, or mitotic checkpoints, apoptosis, or stress response pathways that regulate dauer formation. However, an additional defect in him-10, a kinetochore component, synergized with NHEJ mutations for the radiation-induced developmental phenotypes, suggesting that they may be triggered by mis-segregation of chromosome fragments. Although NHEJ was an important DNA repair pathway for noncycling somatic cells in C. elegans, homologous recombination was used to repair radiation-induced DNA damage in cycling somatic cells and in germ cells at all times. Noncycling germ cells that depended on homologous recombination underwent cell cycle arrest in G2, whereas noncycling somatic cells that depended on NHEJ arrested in G1, suggesting that cell cycle phase may modulate DNA repair during development. We conclude that error-prone NHEJ plays little or no role in DNA repair in C. elegans germ cells, possibly ensuring homology-based double-strand break repair and transmission of a stable genome from one generation to the next. 相似文献
19.
The interaction trap method was used to isolate putative binding partners of Rad16/Pso5, a protein responsible for repair of silent DNA. One of the interactors found was Sgs1, a DNA helicase influencing the life span of Saccharomyces cerevisiae, with homology to the human BLM, WRN and RECQL4 proteins. Using the same fusion proteins from the two-hybrid screening, we show evidence that both proteins also interact in vitro. We tested isogenic strains, containing mutant alleles of the two genes in single and double mutant combination, for phenotypic similarity. Life span in sgs1Delta single and sgs1Delta rad16Delta double mutants is about 40% of that of WT, and the rad16/pso5Delta single mutant also had its life span reduced to 75%. Sensitivity to different mutagens, whose lesions are poorly repaired in rad16/pso5Delta mutants, was tested in sgs1Delta mutants. The sgs1Delta conferred sensitivity to MMS, H2O2 and was moderately sensitive to UV(254nm) (UVC) and 4-NQO. An epistatic interaction between rad16 and sgs1 mutations after UVC, 4-NQO and H2O2 was observed. Moreover, we found that in a top3 background, functional Sgs1p and Rad16p apparently channel MMS, 4-NQO and H2O2 induced lesions into aberrant DNA repair. Our results demonstrate that Sgs1 is not only involved in genome stability, somatic recombination and aging, but is also implicated, together with Rad16/Pso5, in the repair of specific DNA damage. 相似文献
20.
Nucleotide excision repair or polymerase V-mediated lesion bypass can act to restore UV-arrested replication forks in Escherichia coli
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Nucleotide excision repair and translesion DNA synthesis are two processes that operate at arrested replication forks to reduce the frequency of recombination and promote cell survival following UV-induced DNA damage. While nucleotide excision repair is generally considered to be error free, translesion synthesis can result in mutations, making it important to identify the order and conditions that determine when each process is recruited to the arrested fork. We show here that at early times following UV irradiation, the recovery of DNA synthesis occurs through nucleotide excision repair of the lesion. In the absence of repair or when the repair capacity of the cell has been exceeded, translesion synthesis by polymerase V (Pol V) allows DNA synthesis to resume and is required to protect the arrested replication fork from degradation. Pol II and Pol IV do not contribute detectably to survival, mutagenesis, or restoration of DNA synthesis, suggesting that, in vivo, these polymerases are not functionally redundant with Pol V at UV-induced lesions. We discuss a model in which cells first use DNA repair to process replication-arresting UV lesions before resorting to mutagenic pathways such as translesion DNA synthesis to bypass these impediments to replication progression. 相似文献