Comparison of mutagenic and recombinogenic effects of some adenine analogues in Saccharomyces cerevisiae D7

2-Aminopurine, 2-amino-N⁶-hydroxyadenine and N⁶-hydroxyaminopurine were compared in suspension test with growing and non-growing cells for their mutagenic and recombinogenic (reciprocal and nonreciprocal) activities in Saccharomyces cerevisiae strain D7. Ethyl methanesulfonate was used as a positive control. No increases above spontaneous frequencies were observed when non- growing cells were treated with the base analogues although EMS induced concentration- dependent responses at all 3 genetic end-points. When growing cells were treated, HAP was recombinogenic and mutagenic and AHA was mutagenic, but only weakly recombinogenic. HAP induced comparable numbers of revertants at much lower concentrations than AHA. 2AP failed to induce any detectable response even at concentrations as high as 2400 μg/ml.     

Effects of 3-aminobenzamide on Chinese hamster cells treated with thymidine analogues and DNA-damaging agents. Chromosomal aberrations, mutations and cell-cycle progression

The nuclear enzyme, poly(ADP-ribose) synthetase is involved in the repair of damaged DNA. We report here the results obtained with 3-aminobenzamide (3AB), an inhibitor of this enzyme, on induced biological effects. 3AB increases the frequency of chromosomal aberrations induced by DMS, EMS, ENU, bleomycin and CldUrd. The magnitude of the effect is dependent on the type of chemical used, the combinations with DMS and EMS being the most potent ones. No potentiation was observed after treatment of cells with MMC. Mutation frequencies were determined on the HPRT locus and showed that 3AB did not increase the frequency of gene mutations induced by EMS, ENU and CldUrd. Cell-cycle progression is affected when cells are grown in medium containing CldUrd and 3AB, primarily when the inhibitor is present during the second cell cycle when substituted DNA becomes replicated. The extent of the effect depends on the amount of analogue incorporated and is independent of the presence of the analogue in the medium during the second cell cycle. Analysis of chromosomal aberrations in delayed G2 cells with the aid of the premature chromosome-condensation technique revealed numerous aberrations after incorporation of CldUrd and treatment with 3AB.     

Recovery of V79 cell clones with different phenotypes in aminopterin- or azaserine-containing media used for the selection of HGPRT revertants

Three 6-thioguanine (6TG)-resistant mutants were mutagen-treated and selected for clones capable of growing in 2 selective media: HAT medium, containing aminopterin (AP) and HAS medium, containing L-azaserine (AS). Both 6TG-sensitive, wild-type clones and 6TG-resistant mutants were found among colonies growing in HAT medium, while only 6TG-sensitive clones grew in HAS medium. Time for expression was required by 6TG-resistant but not by 6TG-sensitive clones, that were fully expressed immediately after treatment. All HAT-resistant, 6TG-resistant clones which were analyzed proved to be resistant to AP. These data were interpreted as follows: in HAT medium, both HGPRT⁺ revertants and double mutants (HGPRT^?, AP-resistant) were selected, while only HGPRT⁺ revertants were selected in HAS medium. Not all 6TG-resistant mutants were able to produce both classes of HAT-resistant clones.     

Dominant mutations affecting muscle structure in Caenorhabditis elegans that map near the actin gene cluster

By examining F1 progeny of mutagenized Caenorhabditis elegans larvae, we recovered several dominant mutations which affect muscle structure. Five of these new mutations resulted in phenotypes unlike the previously recognized unc-54 and unc-15 dominant alleles. Mapping studies placed all five mutations in the same small region of linkage group V. Polarized light, fluorescence and electron microscopic studies showed that a prominent feature of the disorganized myofilament lattice is the abnormal placement of thin filaments within the body wall muscle cells. Pharyngeal musculature is also affected by three of the mutations when homozygous. Of the five mutations only three are homozygous viable. All three of these have unusually high intragenic reversion rates either spontaneously (~10^?6) or after ethyl methanesulfonate mutagenesis (2 × 10^?5), suggesting that reversion occurs through loss of function mutations. No unlinked suppressor mutations were found. The dominance of the mutations, the effect on thin filaments and the reversion properties suggested that these new dominant mutations lie in a gene or genes specifying a structural component of the thin filament. The positioning of a set of three actin sequences in the same region (Files et al., 1983) led us to speculate that these mutations lie in actin genes.     

甲基磺酸乙酯对水稻花药离体培养效应的研究

本文以粳稻“105”、籼稻“华03"和“鄂早6号”为实验材料,研究了不同浓度化学诱变剂EMS处理对离体培养水稻花药中花粉细胞脱分化与再分化和培养初期花药呼吸作用的影响。结果表明,低浓度EMS能显著提高花药愈伤组织诱导率;高浓度EMS则有明显的抑制作用。EMS对培养初期花药呼吸作用的影响与花药愈伤组织诱导率之间存在明显的平行关系。     

甘蔗体细胞诱变育种研究

用~60Co-γ射线,甲基磺酸乙酯(EMS)处理组培甘蔗愈伤组织,可提高再生植株的变异机率,处理愈伤组织再生植株性状:株高、茎径、锤度等明显偏离正常的正态分布,差异达1%显著标准,EMS处理较~60Co-γ射线变化大。连续试验观察表明:一些变异性状具有遗传性。用~60Co-γ射线或甲基磺酸乙酯处理甘蔗愈伤组织可作为一种甘蔗体细胞诱变育种手段加以利用。     

Mutagenicity of 22 N-nitrosamides and related compounds for Salmonella typhimurium TA1535.

Twenty-two N-nitrosamides and related compounds, including 14 nitrosoureas, 5 nitrosocarbamates, and one nitrosocyanamide, were tested at various concentrations for mutagenic activity towards Salmonella typhimurium TA1535 without the use of microsomes. The ether-water partition coefficient, solubility in water, and half-life in aqueous solution were also measured. Twenty compounds were mutagenic, with "standard mutagenic concentrations" (i.e. those producing 100 mutants/dish) of 0.0024--6500 micron. Standard mutagenic concentration was negatively correlated with the partition coefficient. Three compounds (ethyl 2-acetoxyethylnitrosocarbamate, nitrosocarbaryl, and methylnitrosobenzamide) were more active than the classic mutagen methylnitrosonitroguanidine. Nitrosocarbamates were at least 50 times more mutagenic than the corresponding nitrosoureas. Nitrosodihydrouracil and propylene-nitrosourea were more active than related compounds. Ethylnitrosocyanamide was 730 times more mutagenic than ethylnitrosourea. Fifteen of the test compounds (of which 14 were mutagenic) had previously been assayed in rats for carcinogenicity, all with positive results.     

Relative mutagenicity of antineoplastic drugs and other alkylating agents in V79 chinese hamster cells,independence of cytotoxic and mutagenic responses

The mutagenic and cytotoxic effects of 4 antineoplastic drugs, vinblastine, vincristine, adriamycin and nitrogen mustard and of several monofunctional alkylating agents have been assayed in V79 Chinese hamster cells. Vincristine, vinblastine and nitrogen mustard did not significantly increase the frequency of TG^RHGPRT^? mutants but were all highly cytotoxic. Adriamycin and the monofunctional alkylating agents were all significantly mutagenic even at the lowest doses tested (approx. 70 % survival level). Induced mutant frequency increased linearly with increasing dose whereas dose-response curves for cytotoxicity for these effective mutagens invariably showed a shoulder followed by an exponential decline. At equitoxic doses the relative mutagenic effectiveness was MNU ENU EMS MMS ? DMS. MNU was approx. 20 times more effective than MMS and DMS.Measurement of the total amount of alkylation and the relative amounts of reaction with individual DNA bases at approx. equitoxic doses of MNU and DMS indicated a significantly higher O⁶/N⁷ ratio after MNU (0.15) than after DMS (0.005). However, approx. equal numbers of mutants/10⁵ cells/μM O⁶-Meguanine were induced by these 2 agents. These results support previous conclusions, that mutagenic and cytotoxic responses are independent in V79 cells.     

Fluoride: interaction with chemical mutagens in Drosophila

Simultaneous feeding of sodium fluoride and some chemical mutagens to Drosophila has been reported to reduce the yield of induced mutations compared with feeding the mutagens alone. This observation has been interpreted as a genuine case of antimutagenesis in which fluoride specifically inhibits the induction of chromosome breaks. An alternative hypothesis is that the presence of fluoride inhibits the uptake of the mutagen solutions, producing the same effect as an antimutagen, but for a trivial reason. We have tested this hypothesis using radioactive labelled sucrose to measure the uptake of test solutions. The results show that differential uptake can account for the "antimutagenic" effects reported in Drosophila. Comparison of recessive lethal frequencies induced by Trenimon and PDT do not support the hypothesis that fluoride has any genuine antimutagenic action. Antimutagenic effects of fluoride have been reported in other systems. We cannot exclude the possibility of some genuine effects but we consider that these reports should be critically re-examined in the light of our present findings.