THE LINKAGE OF (1-3)-BETA-GLUCAN TO CHITIN DURING CELL-WALL ASSEMBLY IN SACCHAROMYCES-CEREVISIAE

Pulse-chase experiments with [C-14]glucose demonstrated that in the ce ll wall of wild-type Saccharomyces cerevisiae alkali-soluble (1-3)-bet a-glucan serves as a precursor for alkali-insoluble (1-3)-beta-glucan. The following observations support the notion that the insolubilizati on of the glucan is caused by linkage to chitin: (i) degradation of ch itin by chitinase completely dissolved the glucan, and (ii) disruption of the gene for chitin synthase 3 prevented the formation of alkali-i nsoluble glucan. These cells, unable to form a glucan-chitin complex, were highly vulnerable to hypo-osmotic shock indicating that the linka ge of the two polymers significantly contributes to the mechanical str ength of the cell wall. Conversion of alkali-soluble glucan into alkal i-insoluble glucan occurred both early and late during budding and als o in the ts-mutant cdc24-1 in the absence of bud formation.