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Biomedical subjects

A Nasim

Publications and source records attributed to A Nasim.

At least 91 records · Page 5Linked to original sources
PubMed1978

Mutagenicity and recombinogenicity of daunomycin in Saccharomyces cerevisiae.

The antineoplastic antibiotic daunomycin was tested for mutagenic and recombinogenic effects in haploid and diploid strains of Saccharomyces cerevisiae. This antibiotic failed to induce mutations to lysine and histidine independence in the haploid strain, XV 185-14C, carrying the auxotrophic markers lysl-1 and hisl-7. On the contrary, daunomycin did induce aberrant colonies, including reciprocal products of mitotic crossing over in the diploid strain D7. The results suggest that while daunomycin may be recombinogenic, its mutagenic effects, if any, are either highly specific or negligible. The significance of these results in evaluating the mutagenic/carcinogenic potential of antitumor agents is discussed.

Crossing Over, Genetic↗
PubMed1977

Caffeine enhancement of radiation killing in different strains of Saccharomyces cerevisiae.

Haploid and diploid wild type strains, and three classes of radiation-sensitive mutants of Saccharomyces cerevisiae were tested for enhancement of UV-inactivation by caffeine in growth medium. In addition, the sensitizing effect of caffeine was studied in a haploid and a diploid wild type strain after gamma-irradiation. The drug sensitized the UV-irradiated cells of all strains except those reported to be only slightly UV-sensitive but highly sensitive to ionizing radiation. After gamma-irradiation, no caffeine-enhancement of killing was observed in stationary phase cells of either the haploid or the diploid strain. However, log-phase cells of both strains were partially sensitized. The results of both sets of experiments suggested that caffeine interferes with a recombinational repair occurring in cells in S or G2 phase.

Caffeine↗
PubMed1977

Induction of mutations by chemicals and gamma rays in mutants of yeast refractory to UV-mutagenesis.

Radiation-sensitive mutants of Schizosaccharomyces pombe, known to be refractory to UV-mutagenesis, were tested for mutability caused by treatments with chemicals and gamma rays. One such mutant (rad3) was studied over a wide range of UV doses to compare the kinetics of its mutational response to that of the wild type. All such comparisons were carried out using a forward mutation system. Data show that, unlike UV, the chemical mutagens as well as gamma rays produced mutations (although at reduced frequency), in the strains of S. pombe tested, indicating the existence of an additional mechanism(s) for chemical and gamma ray induced mutations. These observations are discussed as these relate to the pathways for repair of mutational damage in yeast.

Ascomycota↗
PubMed1976

UV-induced lethal sectoring and pure mutant clones in yeast.

The induction of lethal sectoring and pure mutant clones by ultraviolet light has been studied in a homogeneous G1 population of Saccharomyces cerevisiae grown in a normal growth medium. At the lowest UV dose of 250 ergs, which corresponds to a shoulder in the survival curve, all mutants appeared as pure clones. At higher doses the frequency of mosaic mutants progressively increased. These results indicate a relationship between the highest frequency of complete mutants and the maximum repair activity. In addition, the frequency of lethal sectoring at all doses tested was too low to account for the origin of pure mutant clones.

Clone Cells↗
PubMed1976

Temperature-sensitive mutant of Schizosaccharomyces pombe exhibiting enhanced radiation sensitivity.

A conditional lethal and radiation-sensitive mutant of Schizosaccharomyces pombe is described in which both characteristics result from a single gene mutation. Confirmation of the pleiotropic nature of this mutant was obtained by tetrad analysis and by testing the radiation sensitivity of a large number of revertants that grew normally at the restrictive temperature. The colony-forming ability of the mutant after ultraviolet radiation, gamma radiation, and ethyl methane sulfonate treatment is considerably altered by the post-treatment incubation temperature, showing higher survival at 25 than at 30degreesC. The radiosensitivity of the mutant is also influenced by the stage of growth. The difference in radiation sensitivity between the wild type and mutant is greater when log-phase cultures are compared. The characteristics of this mutant suggest that it is defective in a step common to both deoxyribonucleic acid replication and repair.

Ascomycota↗
PubMed1975

Excision of pyrimidine dimers by several UV-sensitive mutants of S. pombe.

Nine radiation-sensitive mutants of S. pombe showing a variety of phenotypic characteristics were analysed for their ability to excise pyrimidine dimers after ultraviolet irradiation. From earlier studies using indirect parameters, it was expected that some would be excision-deficient. Data reported here show that all the mutants tested, like wild type cells, were able to remove a high percentage of pyrimidine dimers during post-irradiation incubation in several different holding media, but not in saline or phosphate buffer. These mutants included strains showing increased, as well as others which showed decreased, levels of UV-induced mutation frequency relative to that of the wild type at the same total dose.

DNA Repair↗
PubMed1975

Genetic control of radiation sensitivity in Schizosaccharomyces pombe.

Genetic analysis of a large number of radiation-sensitive mutants of S. pombe, isolated in different laboratories, showed that these isolates represent 22 non-allelic loci. The mutants were shown to fall into three distinct classes concerning response to UV and ionizing radiation, including two mutants which are primarily sensitive to ionizing radiation but not to UV. Single-gene mutants were crossed to obtain supersensitive double mutants. Such double mutants showed a marked increase in sensitivty to a variety of inactivating agents as compared to the parental strains. The isolation of three classes of radiation-sensitive mutants and the construction of double mutants implies the presence of multiple pathways in S. pombe for repair of radiation-induced damage. The bearing of these data on cellular repair mechanisms in eukaryotes is discussed.

Alleles↗