Mating Pheromones of Saccharomyces kluyveri : Pheromone Interactions Between Saccharomyces kluyveri and Saccharomyces cerevisiae

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Abstract
Saccharomyces kluyveri is a heterothallic yeast with two allelic mating types denoted as a-k and α- k by analogy with Saccharomyces cerevisiae and from the work described here. S. kluyveri produces mating pheromones analogous to those of S. cerevisiae , but which appear to have different specificity. S. kluyveri thus differs from S. cerevisiae, Hansenula wingei , and Schizosaccharomyces pombe in that it exhibits both strong constitutive agglutination and mating pheromones. α- k cells produce a pheromone (“α- k -factor”) which causes a-k cells to arrest in the G1 phase of the cell cycle and to undergo a morphological change. After a period of time dependent on the concentration of α- k -factor, cells exposed to the factor resume cell division. α- k -factor has no effect on a-k /α- k diploids or on α- k cells, but at high concentration does induce G1 arrest of S. cerevisiae a cells ( a -c). a-k cells produce a pheromone (“ a-k -factor”) which causes α- k cells to exhibit a morphological change. In addition, a-k cells exhibit the Bar phenotype with respect to α- k -factor. Partially purified preparations of S. cerevisiae α-factor are more active in inducing G1 arrest of a-k cells than of a -c cells. A more purified preparation of α-c-factor is less active against a-k cells than a -c cells, suggesting that an additional factor (KRE, kluyveri response enhancer) may be lost during purification. Attempts to mate S. kluyveri and S. cerevisiae cells by prototroph selection and by cell-to-cell mating have been unsuccessful with all combinations of mating types. Thus, S. cerevisiae and S. kluyveri are incompatible for mating even though their pheromones exhibit some physiological cross-reaction.