Cell-cell recognition in yeast. Characterization of the sexual agglutination factors from Saccharomyces kluyveri.

Abstract

The cell surface molecules responsible for sexual agglutination between haploid cells of opposite mating type from Saccharomyces kluyveri have been purified and characterized. The 17-factor, released from 17-cells by beta-glucanase digestion (Zymolyase), is a glycoprotein of 6 X 10(4) Da. Its binding activity is heat- and protease-labile, but it is stable to reducing agents and exo-alpha-mannosidase digestion. The 16-factor, released from 16-cells by Zymolyase digestion, has a molecular weight of 5 X 10(5) and is over 95% carbohydrate. An active binding fragment can be released from 16-factor, from the factor purified from a mutant of 16-cells (16(mnn1)-factor), and from the surfaces of the cells themselves by dithiothreitol treatment. The 16(mnn1)-binding fragment has a molecular weight of 2 X 10(4) and is 30% carbohydrate. Its binding activity is stable to heat and some proteases, but it is labile to pronase, carboxypeptidases A and Y, alpha-mannosidases, and mild periodate treatment. 125I-16(mnn1)-binding fragment adheres specifically to 17-cells but does not bind to 16-cells or cells of other yeast strains. The binding of the labeled fragment to 17-cells is characterized by a KA of 10(8) M-1, and 5 X 10(5) binding sites are present per cell. The purified intact factors are monovalent and appear to interact in a lock and key fashion to cause the specific agglutination of S. kluyveri 16- and 17-cells.