Mutants inducible for sexual agglutinability in Saccharomyces cerevisiae

Genetic analysis of inducible sexual agglutination ability in the yeast Saccharomyces cerevisiae

Genetic regulation of the inducibility of sexual agglutination ability in the yeast Saccharomyces cerevisiae was studied. Detailed analysis of the degree of sexual agglutination was carried out; it showed that a greater number of genes are involved in the regulation of inducible sexual agglutination in strain H1-0 than previously assumed. Although dominancy of inducible phenotype over constitutive was confirmed, the effectiveness of one gene changing the constitutive phenotype to the inducible seemed to be somewhat low. Quantity per cell of agglutination substances responsible for sexual agglutination increased as the agglutination ability became greater.

Sexual behavior and its pheromonal regulation in ascosporogenous yeasts

We reviewed our investigations on sexual behaviors and interactions including sexual cell agglutination and pheromone action mainly in non-conventional yeasts, Hansenula anomala, H. wingei, Pichia amethionina, P. heedi, P. opuntiae, Saccharomyces kluyveri, S. globsus, S. exiguus, Saccharomycodes ludwigii. The techniques and genetic models including the cassette model and alpha 1-alpha 2 hypothesis which had been developed largely in S. cerevisiae were applicable to these yeasts in principle. The sexual agglutination was distinctly species-specific while sex pheromones were cross-reactive beyond species' barriers. The successful induction of heterothallic strains from homothallic strains in S. exiguus by mutagenesis enabled to the subsequent biochemical and genetical analysis of sexual behavior in the yeast. The phylogenetic consideration on sex differentiation is also included.

Interspecific actions of alpha mating pheromones on the a mating-type cells of three Saccharomyces yeasts

The alpha mating pheromones synthesized in three Saccharomyces yeasts (S. cerevisiae, S. kluyveri, and S. exiguus) displayed interspecific actions on the a cells of all three species despite the fact that the amino acid sequences of all three alpha pheromones are different. Mating between species, however, did not occur. The interspecific alpha pheromone--a cell reaction was not necessarily more effective than the interspecific one.

Pheromone induction of agglutination in Saccharomyces cerevisiae a cells

a-Agglutinin, the cell surface sexual agglutinin of yeast a cells, was assayed by its ability to bind its complementary agglutinin, alpha-agglutinin. The specific binding of 125I-alpha-agglutinin to a cells treated with the sex pheromone alpha-factor was 2 to 2.5 times that of binding to a cells not treated with alpha-factor. Competition with unlabeled alpha-agglutinin revealed that the increased binding was due to increased cell surface expression of a-agglutinin, with no apparent change in the binding constant. The increase in site number was similar to the increase in cellular agglutinability. Increased expression of a-agglutinin followed the same kinetics as the increase in cellular agglutinability, with a 10-min lag followed by a 15- to 20-min response time. Induction kinetics were similar in cells in phases G1 and G2 of the cell cycle. Maximal expression levels were similar in cells treated with excess pheromone and in cells exposed to pheromone after destruction of constitutively expressed a-agglutinin.

Induction of heterothallic strains and their genetic and physiological characterization in a homothallic strain of the yeast Saccharomyces exiguus

We isolated heterothallic strains from a homothallic strain of S. exiguus by mutagenization with UV or ethylmethanesulfonate (EMS). A gene, not linked to the mating-type locus, was found to control homothallism in the yeast, as in S. cerevisiae. alpha Pheromone of S. exiguus (alpha se pheromone) induced formation of large pear-shaped cells (shmooing) in alpha strains of S. exiguus, S. cerevisiae, and S. kluyveri, and sexual agglutinability of an inducible alpha strain of S. cerevisiae. alpha se Pheromone is a peptidyl substance a little different from alpha pheromone of S. cerevisiae. alpha Pheromone of S. exiguus acts only on alpha cells of S. exiguus. Contrary to the above results, neither sexual agglutination nor zygote formation occurred among these three Saccharomyces yeasts.

Alpha-mating-type-specific suppression and a-mating-type-specific enhancement by tunicamycin of sexual agglutinability in the yeast Saccharomyces cerevisiae

Effects of tunicamycin (TM) on the sexual agglutinability and zygote formation of Saccharomyces cerevisiae were studied using the two kinds of haploid strains, inducible and constitutive for sexual agglutinability. Induction of sexual agglutinability by opposite mating type sex pheromone of inducible strains was inhibited by TM in alpha mating type but not in a mating type. The recovery by temperature-shift-down from the temperature-suppressed sexual agglutinability of constitutive strains was enhanced by TM in a mating type but rather inhibited in alpha mating type. Pretreatment with TM of constitutive strains enhanced sexual agglutinability in a mating type but not in alpha mating type. The above-mentioned a-mating-type-specific agglutinability-enhancing actions of TM were discussed in relation to the action mechanism of alpha pheromone which induces or enhances the sexual agglutinability of a cells. Zygote formation was inhibited by TM in both constitutive and inducible strains at concentrations which showed only partially inhibitory effect on sexual agglutinability.

Selective inhibition of transition from sexual agglutination to zygote formation by ethyl N-phenylcarbamate in Saccharomyces cerevisiae

Effects of ethyl N-phenylcarbamate (EPC) on the mating reaction of Saccharomyces cerevisiae were studied, with special attention on the effect on the alpha pheromone action. EPC inhibited zygote formation at a concentration which promoted induction of sexual agglutinability. EPC enhanced agglutinability induction by alpha pheromone, but inhibited alpha-pheromone-induced formation of large pearshaped cells in a mating type. The enhancement of agglutinability induction was accompanied with increased production of a agglutination substance and inhibition of alpha pheromone inactivation. EPC arrested the cell cycle of a cells probably in the step controlled by CDC19, CDC35, cAMP etc., just before the step controlled by CDC28, alpha pheromone etc.

Changes in production of the mating-type-specific glycoproteins, agglutination substances in association with mating type interconversion in homothallic strains of the yeast, Saccharomyces cerevisiae

Sexual activity in homothallic strains of Saccharomyces cerevisiae was investigated. We succeeded in culturing homothallic haploid cells without conjugation, by lowering the pH value of the culture medium. In spore cultures of a homothallic strain both a and alpha pheromones were detected. Agglutination substance of a and alpha mating types were detected in homothallic haploid cells from spore cultures in early logarithmic phase regardless of mating type information at the HML and HMR loci, but either a or alpha agglutination substance was detected predominantly in homothallic haploid cells from spore culture in late logarithmic phase, depending on mating type information at the HML and HMR loci.

Recessive and dominant genes controlling inducible sexual agglutinability in Saccharomyces cerevisiae

We have characterized the two dominant genes, IND 1 and IND 2, responsible for inducible sexual agglutinability. The strains carrying these genes differ from the inducible strains carrying the recessive gene, saa 1 in the following points. The former strains produce agglutination substance at 22 degree, 28 degree, and 37 degree C only response to sex pheromone of the opposite mating type, but the latter strains produce the substance constitutively without the pheromone at 22 degree C, only in response to the pheromone at 28 degree C, and do not produce the substance, even in the presence of the pheromone, at 37 degree C. We suggest that strains carrying one of the dominant, inducible genes are wild type and have a pheromone-controlled regulatory system of sexual agglutinability.