2 SPORULATION-SPECIFIC CHITIN DEACETYLASE-ENCODING GENES ARE REQUIREDFOR THE ASCOSPORE WALL RIGIDITY OF SACCHAROMYCES-CEREVISIAE

The formation of the ascospore wall of Saccharomyces cerevisiae requir es the coordinate activity of enzymes involved in the biosynthesis of its components such as chitosan, the deacetylated form of chitin, We h ave cloned the CDA1 and CDA2 genes which together account for the tota l chitin deacetylase activity of the organism. We hare shown that expr ession of these genes is restricted to a distinct time period during s porulation. The two genes are functionally redundant, each contributin g equally to the total chitin deacetylase activity. Diploids disrupted for both genes sporulate as efficiently as wild type cells, and the r esulting mutant spores are viable under standard laboratory conditions . However, they fail to emit the natural fluorescence of yeast spores imparted by the dityrosine residues of the outermost ascospore wall la yer. Moreover, mutant spores are relatively sensitive to hydrolytic en zymes, ether, and heat shock, a fact that underscores the importance o f the CDA genes for the proper formation of the ascospore wall.