ISSN:0893-6692    

DOI:10.1002/em.2850110402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThis manuscript has been reviewed by the Health Effects Research Laboratory, U.S. Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

ISSN:0893-6692    

DOI:10.1002/em.2850110403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0893-6692    

DOI:10.1002/em.2850110404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0893-6692    

DOI:10.1002/em.2850110405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractHoechst 33258 fluorescence of single stranded DNA has been used to perform alkaline elution with unlabeled DNA. The high background fluorescence of “standard” elution solutions has prompted others to use EDTA but the elution characteristics of DNA in EDTA‐containing solutions and the comparability of results with those using “standard” tetrapropyl ammonium hydroxide solutions have not previously been examined. We report here the elution characteristics of DNA in EDTA and the relevant parameters for the successful use of EDTA as an elution solution. An increase in elution pH to 12.4 is required but elution solutions of higher pH cause alkaline hydrolysis of undamaged DNA. Drug‐treated DNA from which DNA‐protein crosslinks have been removed can be completely removed from the filters at the end of the elution by a Pronase filter digestion. The simplest and most efficient removal of DNA‐protein crosslinks is through the inclusion of proteinase‐K in an SDS containing lysis solution. EDTA elution can measure interstrand crosslinks and single strand breaks as easily as is performed using radiolabeled DNA under “standard” elution conditions and requires only 1.5–2 × 106cells per elution filter. DNA‐protein crosslinking measurements were unsatisfactory, however, since even the Pronase digestion failed to completely remove protein‐crosslinked DNA from the elution filters.Portions of this work were presented at the 77th Meeting of the American Association f

ISSN:0893-6692    

DOI:10.1002/em.2850110406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractPrevious DNA sequence analysis of bleomycin‐induced forward mutations in repackaged lambda phage has suggested SOS‐dependent replicative bypass of oxidized apyrimidinic sites as a possible mechanism of mutagenesis. In order to evaluate this hypothesis further, frequencies of mutation to a clear‐plaque phenotype were compared for bleomycin‐damaged phage grown in various repair‐deficient strains ofEscherichia coli. Survival of bleomycin‐damaged phage was virtually identical in all host strains. Studies in SOS‐deficient strains indicated specific requirements for functionalrecA+andumuC+alleles in the generation of the majority of bleomycininduced mutations, as well as a less stringent requirement for induction of the SOS response by ultraviolet irradiation of the host cells. These results are expected for mutagenesis resulting from apyrimidinic sites. However, the mutation frequency for bleomycin‐damaged phage was the same whether the phage were grown in a wild‐type strain or in strains deficient in apurinic/apyrimidinic repair endonucleases; this was true even for annth∼nfo∼xth∼ strain lacking all three major apurinic/apyrimidinic endonucleases (endonuclease III, endonuclease IV, and exonuclease III). Likewise, phage grown in an endonuclease IV‐overproducing strain showed the same mutation frequency as those grown in wild‐type cells. These data suggest that either i) bleomycin‐induced mutagenesis results from SOS‐dependent bypass of lesions other than apyrimidinic sites or ii) the number of apyrimidinic sites available for SOS processing is virtually independent of the level of apurinic/apyrimidinic endonuclease activity in the cell. It is possible that a fraction of the apyrimidinic sites induced by bleomycin either are intrinsically resistant to repair or undergo secondary react

ISSN:0893-6692    

DOI:10.1002/em.2850110407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe DNA adducts and mutational profile produced by N‐nitroso‐N‐ethylurea (ENU) inSalmonellaare examined. The adduct profile produced by ENU in isolated DNA and at two doses inSalmonellawere similar, with one exception: O6‐ethylguanine (O6‐EtG) was not detected at the low dose inSalmonella. This adduct was presumably repaired by a constitutive repair system. The premutagenic adducts, O2‐ethylthymidine (O2‐EtdT) and O4‐ethylthymidine (O4‐EtdT) were detected, with the former adduct present at higher levels. The mutational profile was also determined at the same doses by utilizing a system involving a series of histidine auxotrophs ofSalmonellawith differing mutagenic specificities and a further subclassification of the revertants. Four different patterns of mutagenesis were observed; these were dependent on dose and on the presence or absence of the plasmid pKM101. The mutational spectrum produced at the higher dose in strains without the plasmid consisted mainly of GC→AT transitions. At the high dose, in strains harboring pKM101, three base changes contributed importantly to the mutational spectrum: GC→AT, AT→GC, and AT→CG. At the low dose in the strains without pKM101, little mutagenesis was observed, and in strains containing pKM101, mutagenesis was greatly enhanced with the most frequent mutations resulting from AT→GC and AT→CG base changes. O6‐EtG was presumably responsible for the bulk of the GC→AT transitions at the high dose. Calculations and evidence are presented indicating that O2‐EtdT is responsible for at least some of the mutagenesis that occurs at AT base pairs. O4‐EtdT and O2EtdT are probably responsible for a major fraction of the AT→GC transitions, and we suggest that error‐prone repair activity acting on O2‐EtdT and/or

ISSN:0893-6692    

DOI:10.1002/em.2850110408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractWhen mammalian cells are lysed in 2% sodium dodecyl sulphate detergent followed by addition of an equal volume of 0.12 M potassium chloride, a precipitate forms that can be collected by low‐speed centrifugation. This precipitate contains the cell protein and nucleic acid in close association with protein. In die absence of DNA damage, most of the DNA precipitates, but when DNA strand breaks are created by exposing cells to ionizing radiation or toxic chemicals, DNA is released from the protein and remains in the supernatant after centrifugation. The proportion of DNA remaining in the supernatant is thus a measure of the amount of DNA damage. This assay is characterized in terms of optimum cell number and pH and dose‐response curves for DNA damage and cell survival following ionizing radiation, MNNG, BCNU, and VP‐16 are shown. Sensitivity, simplicity, speed, and large sample handling capacity should allow wide application of this new assay to a variety of questions concerning DNA damage and r

ISSN:0893-6692    

DOI:10.1002/em.2850110409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThree genotoxic carcinogens and eight tumor promoters were tested for induction of aneuploidy, specifically chromosome loss, inSaccharomyces cerevisiaeD61.M. This is a heterozygous diploid yeast strain that permits the scoring of segregants expressing three linked recessive markers (cyhR2, ade6, andleul), two of which (ade6andleul) are located close to the centromere on opposite arms of chromosome VII. The centromere markerleuwas routinely checked, and a positive control (bavistan) was run with every experiment. The three genotoxic carcinogens aflatoxin B1, benzo(a)pyrene, and 7,12‐dimethylbenz(a)anthracene did not induce aneuploidy, independent of the presence or absence of an exogenous metabolic activation system (rat liver homogenate; S9). Four of the eight tumor promoters tested induced chromosome loss but no mitotic recombination or mutation: cholic acid, lithocholic acid, phenobarbital, and saccharin. Diethylstilbestrol (DES) led to positive as well as to negative results in several independent experiments. In the case of the positive experiment, DES also induced putative recombinants. Three tumor promoters induced neither chromosome loss nor mitotic recombination: anthralin, 4,4′‐dichloro‐diphenyl‐ethane (DDT) and γ‐hexachlorcyclohexane (lindane). From our experiments it can be concluded that the hypothesis put forward by Parry et al. [Nature; 294:263–265], according to which tumor promoters induce chromosome loss in yeast, is not correct in a general sense. In our set of eight tumor promoters, only one half distinctly induced c

ISSN:0893-6692    

DOI:10.1002/em.2850110410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractLaboratory models were used to study the inhibition of mutagen formation by Maillard‐type reactions during cooking of meats or fish. The amino acid L‐proline (L‐pro) was an effective, dose‐dependent inhibitor of the development of mutagenicity (Ames test) in a liquid‐reflux model of glucose + glycine + creatinine known to produce IQ‐type mutagens (MeIQxand 7,8‐DiMeIQx). L‐pro also inhibited formation of mutagens in a reflux model of threonine + creatinine, developed in our laboratory, which yields a novel class of IQ‐“like” aminoimidazol‐4‐one mutagens. A mixture of L‐pro and L‐tryptophan (L‐trp) at lower concentrations of each yielded increased inhibition, compared with the findings when each

ISSN:0893-6692    

DOI:10.1002/em.2850110411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY