Masao Yoshimura

Temperature-dependent conversion of sexual agglutinability in Saccharomyces cerevisiae

SummaryTemperature dependency of sexual agglutinability in Saccharomyces cerevisiae was found. In almost all strains tested that were derived from several different sources, the agglutinability was constitutive when grown at 25° C but inducible when grown at 36° C, suggesting that the temperature-dependent conversion of sexual agglutinability is general nature in Saccharomyces. Cycloheximide and 8-hydroxyquinoline inhibited completely both cell division and the conversion of the agglutinability from constitutive to inducible type. N-Hydroxyurea and 5-fluorouracil which allowed cell growth to some extent inhibited the conversion slightly. Hence, the conversion of the agglutinability from constitutive to inducible type may be achieved in cells newly born after temperature shift. The reverse conversion of the agglutinability was gradual in comparison with the conversion from constitutive to inducible type. This conversion of the agglutinability was regulated by a single gene closely linked to mating type locus, which is recognizable by using a temperature-independent constitutive strain.

Temperature-sensitive loss of sexual agglutinability in Saccharomyces cerevisiae.

Temperature dependency of sexual agglutination in Saccharomyces cerevisiae was found. Of 31 strains tested, which showed normal agglutination when cultured at 25°C, 29 strains lost their sexual agglutinability when they were grown at 37°C.

Plasminogen phenotypes in a Japanese population. Four new variants including one with a functional defect.

Human plasminogen (PLG) phenotypes were investigated by polyacrylamide gel isoelectric focusing followed by immunoblotting. In 5,735 plasma samples from unrelated, healthy Japanese individuals, four new variants were detected and tentatively designated PLG AOsaka, PLG BOsaka, PLG MOsaka and PLG ANara. The plasminogen concentrations and activities of the PLG phenotypes were studied. In agreement with previous studies PLG M5 was found to have a decreased activity. The new variant PLG MOsaka had a very low activity and appears to be an abnormal plasminogen with a functional defect similar to that of PLG M5.

Chloroquine, a lysosomotropic agent, inhibits zygote formation in yeast

Haploid cells of opposite mating type of Saccharomyces cerevisiae conjugate to form zygote. During the conjugation process, the degradation or reorganization of the cell wall and the fusion of the two plasma membranes take place. Since chloroquine inhibits cellular events associated with the reorganization of the plasma membrane, the effect of the drug on conjugation was studied. Chloroquine at a concentration, at which cell growth was not retarded, inhibited zygote formation, while it did not affect other mating functions, such as sexual agglutination, production of and response to mating pheromone. Cells in a mating culture containing chloroquine formed no “prezygote” suggesting that they were not prepared for entering into fusion process. The inhibitory effect of chloroquine was reversible as cells formed zygote when they were washed after treatment with chloroquine. Zygote formation was unaffected in cells possessing chlorquine within vacuoles after incubation with the drug in complete medium (YPD) at pH 7.5, followed by washing. This suggests that chloroquine inhibits zygote formaton by adsorbing to the plasma membrane of S. cerevisiae.

Induction of sexual cell agglutinability of a mating type cells by α-factor in Saccharomycescerevisiae

Abstract Mating hormone, α-factor, which inhibits DNA synthesis and causes characteristic changes in cell morphology in a mating type cells, was also responsible for induction of sexual cell agglutinability of a mating type cells.

Arachidonic and oleic acids stimulate zygote formation in the presence of mating pheromone in the yeast, Saccharomyces cerevisiae

Effect of exogenous fatty acids on zygote formation in Saccharomyces cerevisiae was studied. Arachidonic and oleic acids considerably stimulated zygote formation, but other fatty acids tested, linoleic, linolenic, stearic and palmitic acids, did not. Pretreatment experiments with arachidonic acid showed that the stimulation of zygote formation by the fatty acid required the presence of mating pheromone.

An α-specific gene, SAG1 is required for sexual agglutination in Saccharomyces cerevisiae

SummarySeven α-specific mutants specifically defective in sexual agglutinability were isolated. The other α mating functions exhibited by these mutants, designated sag mutants, such as the production of α pheromone and response to a mating pheromone, were normal. While the MATα sag1 cells did not agglutinate with wild-type a cells, the MATα sag1 cells did, indicating that the SAG1 gene is expressed only in α cells. The mutations were semi-dominant and fell into a single complementation group, SAG1, which was mapped near met3 on chromosome X. Complementation analysis showed that sag1 and aga1, the latter being a previously reported α-specific mutation, were mutations in the same gene.

Induction of sexual agglutinability by unsaturated fatty acids in Saccharomyces cerevisiae

Agglutinins in S. cerevisiae are necessary for mating, for recognition between cells of opposite mating type. The mode of agglutinin synthesis is altered by the growth temperature and by the carbon source, from constitutive to inducible synthesis and vice versa. Some of the unsaturated fatty acids tested induced synthesis of agglutinins in cells grown at an elevated temperature, even in the absence of the pheromone. However, synthesis of agglutinins in glycerol-grown cells, that are inducible by the pheromone, was not induced by linolenic acid. Hence, the change in the mechanism of regulation of agglutinability produced by differences in temperature probably differs from that produced by differences in carbon source.

A mutation affecting sexual agglutinability in MATα locus of Saccharomyces cerevisiae.

SummaryA temperature-sensitive non-agglutinative mutant of Saccharomyces cerevisiae was isolated and characterized. The mutation, sag2, affected sexual agglutination, conjugation and production of α-mating pheromone at a restrictive temperature, but not the response to α-mating pheromone. Genetic analyses showed that the mutation was recessive and in the MATα locus. The sag2 mutation complemented with matα2 but not with matα1 These results suggest that sag2 is in the MATα1 gene and that at a restrictive temperature the mutation, sag2, inactivated the MATα1 product, a positive regulator of α-mating functions. The sag2 mutation is like matα1-5 in its retention of response to α-mating pheromone. However, at 25 °C, sag2 cells were competent to mate, whereas matα1-5 cells were not. Hence, sag2 is regarded as a new allele in the MATα1 gene, which we designate matα1-11.