共查询到20条相似文献,搜索用时 15 毫秒
1.
Gary J. Smith David G. Kaufman Joe W. Grisham 《Biochemical and biophysical research communications》1980,92(3):787-794
The excision of N7-methylguanine (N7-meGua) and O6-methylguanine (O6-meGua) lesions in DNA caused by treatment of cells with N-methyl-N′-nitro-N-nitrosoguanidine was evaluated as cells synchronously traversed the pre-S and S phases of the cell cycle. Proliferation of cells was arrested by growth to confluence, then cells were treated with MNNG and released into a synchronous cell cycle by replating at lower density. The frequency of the two methylated guanines (methylated guanines/106 guanines) was determined at the time of replating, immediately prior to the onset of S phase and at the conclusion of S phase. During the pre-S interval N7-meGua and O6-meGua were lost at rates consistant with the reported biological half-lives of 26–28 hr and 20–21 hr, respectively. In contrast, when the reduction in frequency of methylated guanines was determined for the S phase it was found that the apparent decrease could be explained by the increased DNA content of the cultures resulting from DNA replication. 相似文献
2.
DNA strand scission by the antitumor protein neocarzinostatin 总被引:5,自引:0,他引:5
The antibiotic protein, neocarzinostatin, induces the scission of DNA strands and . HeLa cell DNA prelabelled with [14C] thymidine is cut into large pieces with a peak at 80–90S when cells are incubated with 0.5 to 5.0 μg/ml of highly purified neocarzinostatin. Incubation of the antibiotic (0.5 μg/ml) with [3H] SV40 DNA in the presence of 2-mercaptoethanol results in the conversion of superhelical DNA I to nicked circular duplex DNA II. At high levels of drug, smaller fragments of linear DNA are produced. Strand breaks are detected in both neutral and alkaline sucrose gradients, indicating that drug susceptibility is not due to alkali-labile bonds. 相似文献
3.
When different strains of are exposed to Cd2+, the cells accommodate after a long lag and proliferate. The time required for this response depends on the nature of the strain and the supplements in the growth medium. Immediately after exposure to Cd2+, considerable single strand breaks in the DNA are observed but the DNA is repaired prior to the initiation of cell proliferation. The finding that accommodation occurs in DNA polymerase I-deficient mutant cells suggests that DNA polymerase I may not be required for repair of damaged DNA in Cd2+-exposed cells. The recovery of Cd2+-exposed cells in a temperature-sensitive DNA ligase mutant cells at the permissive temperature (30° C) and failure to recover at the non-permissive temperature (42° C) indicates, however, that DNA ligase is involved in the repair of the single strand breaks associated with Cd2+-induced damage. 相似文献
4.
Chang human liver cells were treated with the carcinogens N-methyl-N′-nitrosoguanidine (MNNG) and nitrosomorpholine (NM). In addition, cells were exposed to the folic acid analog, 2-hydroxy-N10 nitrosofolic acid. Repair of the damage to DNA was estimated by selective photolysis of BUdR-containing repaired regions with 313 nm radiation. The influence of the co-carcinogen Arlacel A was estimated with the three compounds. Results indicated significant repair synthesis with MNNG- and NM-treated cells. 2-Hydroxy-N10 nitrosofolic acid elicited no damage to the liver DNA. Arlacel A prevented repair synthesis in cells treated with NM and MNNG. 相似文献
5.
S F Jackson B R Wentzell D R McCalla K B Freeman 《Biochemical and biophysical research communications》1977,78(1):151-157
L(+)--chloramphenicol induces reversion of His? strains TA100 and TA1535 in the conventional Ames' assay without microsomal activation. Any mutagenicity of D(?)--chloramphenicol was masked by toxicity. Similarly, a sensitive fluctuation test showed mutagenesis with L(+)--chloramphenicol at concentrations of 0.5 μM and above but the D(?) isomer proved to be toxic even at these low levels. The L(+) isomer caused single strand breaks in the DNA of and strains TA1535, TA100 and TA1976. The D(?) isomer caused breaks in and TA1976 although it was less effective and it did not produce DNA breaks in TA1535 or TA100. 相似文献
6.
W.A. Deutsch A.L. Spiering G.R. Newkome 《Biochemical and biophysical research communications》1980,97(3):1220-1226
The -isomer of the antitumor drug dichlorodiammineplatinum(II) [-Pt(II)] was tested for its abilty to introduce nicks (single-strand breaks) into supercoiled PM2 DNA. Whereas incubations up to 24 h show no indication of -Pt(II)-treated DNA having single-strand breaks, DNA interstrand cross-links were detected in the first 15 min of incubation. Furthermore, the formation of DNA interstrand cross-links was inhibited and fully reversed after incubation with 2 mM thiourea. 相似文献
7.
8.
Arsenic compounds are known carcinogens. Although many carcinogens are also mutagens, we have previously shown that sodium
arsenite is not mutagenic at either the Na+/K+ ATPase orhprt locus in Chinese hamster V79 cells. It can, however, enhance UV-mutagenesis. We now confirm the nonmutagenicity of sodium
arsenite in line G12, a pSV2gpt-transformed V79 (hprt
−) cell line, which is able to detect multilocus deletions in addition to point mutations and small deletions. The lack of
arsenic mutagenicity has led to studies emphasizing its comutagenicity. Sodium arsenite at relatively nontoxic concentrations
(5 μM for 24 h or 10 μM for 3 h) is comutagenic withN-methyl-N-nitrosourea (MMU) at thehprt locus in V79 cells. Using a nick translation assay, which measures DNA strand breaks by incorporating radioactive deoxyribonucleoside
monophosphate at their 3′OH ends in permeabilized cells, we found that much more incorporation was seen in cells treated with
MNU (4 mM, 15 min) followed by 3-h incubation with 10 μM sodium arsenite compared with cells exposed to the same MNU treatment followed by 3-h incubation without sodium arsenite.
This result shows that in the presence of arsenite, strand breaks resulting from MNU or its repair accumulate over a 3-h period.
We suggest that the repair of MNU-induced DNA lesions may be inhibited by arsenite either by affecting the incorporation of
dNMPs into the MNU-damaged DNA template or by interfering with the ligation step. 相似文献
9.
The clastogenic effect ofN-methyl-N′-nitro-N-nitrosoguanidine (MNNG) in Chinese hamster ovary (CHO) cells and its modulation by Na2SeO3 and caffeine were studied by metaphase analysis of chromosome aberrations (CA) as well as by measuring the formation and
repair of single-strand (ss) DNA breaks employing hydroxylapatite chromatography. Treatment of CHO cells with MNNG (1.25 or
2.5 × 10-5M) for 3 h caused CA in 11 and 19% of metaphases scored, respectively. Pretreatment of cells with Na2SeO3 (1–5 μg/mL) or caffeine (0.2–2.0 mg/mL) for 2 h resulted in a 2–3.5-fold increase of CA frequency. Addition of both modulators
during the mutagen exposure tended to cause a slight inhibition of clastogenic activity of MNNG (1.25 × 10−5
M) or had no effect on CA number when MNNG was used at a concentration of 2.5 × 10−5M. Posttreatment of CHO cells with Na2SeO3 for 20 h after MNNG was ineffective in influencing the number of metaphases with CA, whereas, at these conditions, caffeine
enhanced up to 6-7-fold the clastogenic activity of MNNG. Addition of both modulators during the whole experiment, 2 h pretreatment
included, resulted in a further significant increase of CA frequency up to the total pulverization of chromosomes in all metaphases
scored. The coclastogenic effect of caffeine was greater in this case. The enhancement of chromosome-damaging activity of
MNNG by selenite and caffeine was better expressed when this carcinogen was applied at the higher concentration used. An additive
coclastogenic effect was observed in CHO cells treated simultaneously with Na2SeO3 and caffeine plus MNNG. In addition, the treatment of CHO cells with MNNG (5 × 10−6
M) caused a rapid increase of ssDNA breaks number reaching maximal values after 30–45 min. However, up to 50–60% of MNNG-induced
ssDNA breaks were repaired during the first 60–150 min after the mutagen exposure. The 2 h pretreatment of CHO cells with
Na2SeO3 (2 μg/mL) or the addition of this trace element after MNNG had no effect on formation and repair of MNNG-induced ssDNA breaks.
The coclastogenic effect of Na2SeO3 in CHO cells treated with MNNG was not directly linked to the induction and disappearance of ssDNA breaks measured by hydroxylapatite
chromatography. 相似文献
10.
Mitsumasa Okamoto Hideo Yamagishi 《International journal of biological macromolecules》1981,3(2):105-113
In a previous study, various intermediates in λ DNA packaging were visualized after lysis of λ-infected cells with osmotic shock and sedimentation through a sucrose formalin cushion onto electron microscope grids. Along this line, a systematic screening for intermediates accumulated in all head mutants available was performed. λA?-infected cells accumulate only empty spherical protein shells (petit λ) bound at an intermediate point along the DNA thread. In situ digestion experiments with restriction endonuclease EcoRI show that the petit λ-DNA complexes are formed at a fixed point on the DNA concatemer. In cells, however, most petit λ was not bound to DNA. In Fec? cells, which are defective in formation of concatemers but normal in head protein synthesis, most petit λ did not sediment onto the carbon film of the grid. In mutant, petit λ, partially full heads and empty heads with released DNA were observed. λFI?-infected cells also accumulate petit λ and partially full heads. The present studies suggest that protein pNu1 is required for complex formation between head precursors and DNA concatemers, for the initiation of DNA packaging, and I for the promotion of DNA packaging, and for stabilization of head structures. The results obtained with other head mutants involved in formation of mature proheads and head completion confirm earlier results obtained by different techniques. 相似文献
11.
F.R. Serna I.I. Samoylenko 《Biochemical and biophysical research communications》1975,67(4):1415-1421
The existence of the super fast repairing system for single-strand breaks in DNA, induced in cells exposed to gamma-irradiation at 0°C in a phosphate buffer under aerobic conditions, has been shown in three strains of Escherichia coli K-12 (AB 1157 , AB 2463 and JC 4457 ). Super fast repairing system rejoins up to 90–95 % of initial single-strand breaks during irradiation. An estimation of the lower limit of the rate of repairing the breaks by this system has been made. 相似文献
12.
B I Sinzinis G B Smirnov A A Saenko 《Biochemical and biophysical research communications》1973,53(1):309-316
The effect of ultraviolet irradiation (UV) has been studied in mutator UV-sensitive mutant , its derivative and wild-type strain. The mutant is about 5 times more UV-sensitive than the + isogenic strain, but 3 times less sensitive than the single mutant. Cells of the mutant are unable to rejoin the fragments of parental DNA formed after UV as a result of incision. The double mutant as well as the single mutant irradiated with UV is unable to introduce breaks into parental DNA. The extent of postreplication repair is essentially normal in the cells. There is no significant difference between the and cells in the rate and extent of UV-induced DNA degradation. 相似文献
13.
The state of the structural integrity of the DNA from mouse myocardial cells has been investigated by utilizing both CsCl density gradient sedimentation and digestion by S1 endonuclease from . The DNA from myocardial cells of young mice sedimented in a narrow peak at the expected density of 1.701 g/cm3, while the DNA from the heart cells of senescent mice became broadly distributed in CsCl gradients, banding even more multimodally in alkaline sucrose gradients. This mode of sedimentation indicates that old mouse DNA becomes partially fragmented. When the native DNA of myocardial cells from 6, 20 and 30 month old mice was treated with single-strand specific S1 endonuclease, it was the DNA from the senescent mice that showed a progressive increase in sensitivity to digestion by the enzyme. The results indicate that the heart DNA of aging mice develops single-stranded gaps in addition to a breakdown into differently sized fragments. 相似文献
14.
DNA polymerase activities in cell-free lysates of unfertilized eggs, larvae and immature ovaries of were compared to purified DNA polymerase I using several natural and synthetic templates. The templates were tested as the native and denatured forms of normal and DNase I treated molecules. Although the polymerases tended to prefer DNase I treated Xenopus DNA over the other templates tested, so did the polymerase I. In general, the template preferences of the polymerases studied depended in complex ways on both the form and the species of origin of the template. 相似文献
15.
Action of the S1 endonuclease from Aspergillus oryzae on simian virus 40 supercoiled component I DNA 总被引:11,自引:0,他引:11
M Méchali A M de Recondo M Girard 《Biochemical and biophysical research communications》1973,54(4):1306-1320
The digestion products of superhelical component I of SV40 DNA incubated with various concentrations of nuclease S1 from , an enzyme specific for single-stranded nucleic acid, were studied. The enzyme shows a preference for supercoiled DNA I as opposed to relaxed DNA II molecules, and converts SV40 DNA I into linear molecules. Conditions have been developed under which the majority of SV40 DNA I molecules is converted into form II DNA. By using high concentrations of enzyme, it was possible to introduce further breaks in the DNA molecule; by increasing ionic strengh or using SDS this activity was not eliminated. 相似文献
16.
Activation of the template activity of isolated rat liver nuclei for DNA synthesis and its inhibition by NAD 总被引:6,自引:0,他引:6
The template activity of isolated rat liver nuclei for DNA synthesis assayed with DNA polymerase was found to be dependent upon the presence of Ca2+ or Mg2+ in the incubation medium. DNA was prepared from isolated nuclei subjected to conditions which activated the template and centrifuged in an alkaline sucrose gradient. The distribution profile showed that smaller fragments were formed, suggesting enhancement of endonucleolytic activity. When isolated nuclei were incubated with NAD to induce poly(adenosine diphosphate ribose) formation and were subjected to the activation conditions, the template for DNA synthesis remained unchanged. The distribution profile in an alkaline sucrose gradient of DNA prepared from these nuclei and control nuclei was identical. The present findings suggest that the template-activating system for DNA synthesis was blocked when isolated nuclei were treated with NAD . 相似文献
17.
α factor is a diffusible substance produced by cells of the mating type which inhibits cell division (1) and the initiation of nuclear DNA synthesis (2) in cells of the mating type. In this report, it is shown that mitochondrial DNA synthesis continues at a normal rate in cells for at least 6 hours in the presence of α factor, resulting in a 5-fold increase in the amount of mitochondrial DNA per cell. The continued synthesis of mitochondrial DNA in the absence of nuclear DNA synthesis allows specific labeling of yeast mitochondrial DNA. 相似文献
18.
The relationship between cell fusion, DNA synthesis and the cell cycle in cultured embryonic normal and dysgenic () mouse muscle cells has been determined by autoradiography. The experimental evidence shows that the homozygous mutant myotubes form by a process of cell fusion and that nuclei within the myotubes do not synthesize DNA or undergo mitotic or amitotic division. The duration of the total cell cycle and its component phases was statistically the same in 2-day normal and mutant () myogenic cultures with the approximate values: T, 21.5 hr; G1, 10.5 hr; S, 7.5 hr; and G2, 2.5 hr. In both kinds of cultures, labeled nuclei appeared in myotubes 15–16 hr after mononucleated cells were exposed to [3H]thymidine, and the rate of incorporation of labeled nuclei into multinucleated muscle cells was comparable in control and dysgenic cultures. Thus, homozygous muscle cells in culture are similar to control cells with respect to their mechanism of myotube formation and the coordinate regulation of DNA synthesis and the cell cycle during myogenesis. 相似文献
19.
Strand resealing in the excision repair of 5,6-dihydroxy-dihydrothymine in osmium tetroxide oxidized polyd(A-T) by crude extracts is accomplished by polynucleotide ligase. Osmium tetroxide oxidized polyd(A-T)_serves as a chemically well defined model substrate containing damage of the kind introduced into DNA by ionizing radiation. In the first incision step of excision repair approximately one endonucleolytic nick is introduced into the polymer by extracts of endoI? and endoI?A6? per ring damaged thymine residue removed. 相似文献
20.
《Mutation Research/Genetic Toxicology》1996,367(3):151-159
Since alkylating agents are widely present in the environment and constitute a continuous challenge to genome integrity, cells and organisms have developed defense mechanisms to remove such lesions. We monitored the response of human keratinocytes to a very low concentration of a methylating agent, namely 2.5 nM N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). The effect of a 60-min exposure of quiescent cells to 2.5 nM MNNG was studied in terms of DNA integrity, poly(ADP-ribose) metabolism, clonogenic survival and DNA synthesis. We observed two waves of DNA strand break formation and resealing. Interestingly, the amount of DNA strand breaks in exposed cells was lower than in unexposed control cells. This phenomenon was also observed when cells were exposed to MNNG in the presence of a protein synthesis inhibitor, or when they were maintained on ice during the treatment. A dose of 2.5 nM MNNG stimulated poly(ADP-ribose) turnover, reduced the intracellular NAD+ content, stimulated DNA synthesis and caused a remarkable increase in clonogenic survival. Thus, the cellular responses to extremely low concentrations of MNNG differ sharply from those observed at higher doses of this carcinogen. We conclude that the very low dose response cannot be extrapolated from usual dose-response analyses. 相似文献