Sexual agglutination substances require a 'carrier' glycoprotein for integration into the cell wall of Saccharomyces...

Sexual agglutination, caused by agglutination substance (AS) on a and alpha cell walls, is the first indispensable step of the mating reaction in ascosporogenous yeasts including Saccharomyces cerevisiae. The AS biosynthetic process in S. cerevisiae was investigated by pulse label-chase experiments with analysis by polyacrylamide gel electrophoresis (PAGE) for 16 h in the presence of urea. Because of its low mobility, AS can be separated from other proteins by prolonged PAGE. Nascent AS was integrated into cell walls after it linked covalently to a 'carrier' glycoprotein. The results suggest that the 'carrier' is synthesized stepwise through three distinct precursors (III-->II-->I). The 'carrier' glycoprotein (I) and its precursors (II, III) were synthesized in both a, alpha haploid and a/alpha diploid cells. The N-glycosylation linkage inhibitor, tunicamycin, and protein synthesis inhibitor, puromycin, inhibited the III to I maturation. The results indicated that both the 'carrier' and the nascent active site of AS linked to the 'carrier' are integrated into the wall in a haploid cell while the 'carrier' alone is integrated in a diploid cell.