Chapter 10 Induction of Haploid Glycoprotein Mating Factors in Diploid Yeasts

This chapter discusses induction of haploid glycoprotein mating factors in diploid yeasts. It illustrates the steps in the alternation of generations of Hansenula wingei , a heterothallic yeast. The two opposite mating types are haploid strains 5 and 21. Both haploids are constitutively agglutinative and, while cell suspensions of each are stable separately, they agglutinate immediately when mixed together. Following agglutination, the cells conjugate pairwise, producing a 5 × 21 diploid hybrid which is nonagglutinative and a nonmater. The diploid can be either grown vegetatively or sporulated if transferred to special media. The sporulation process results in a tetrad of meiotic products: two spores of mating type 5 and two spores of mating type 21, indicating that these mating types are allelic. In the chapter, methods are presented that alter one step of the normal life cycle—the mating response of the diploid. Conditions are discussed that induce the diploid to become sexually agglutinative and therefore able to participate in the first step in conjugation–cellular recognition. Biology of the yeast H. wingei and control of haploid-mating functions in the diploid are discussed. Significance of induction of sex-specific cell surface glycoproteins in the diploid is also discussed.