Chitinase is required for cell separation during growth of Saccharomyces cerevisiae

The Saccharomyces cerevisiae chitinase described by Correa et al. (Correa, J. U., Elango, N., Polacheck, I., and Cabib, E. (1982) J. Biol. Chem. 257, 1392-1397) has been cloned and sequenced. Analysis of the derived amino acid sequence suggests that the protein contains four domains: a signal sequence, a catalytic domain, a serine/threonine-rich region, and a carboxyl-terminal domain with high binding affinity for chitin. Most of the enzyme produced by cells is secreted into the growth medium and is extensively glycosylated with a series of short O-linked mannose oligosaccharides ranging in size from Man2 to Man5. Chitinase O-mannosylation was further examined in the temperature-sensitive secretion mutants sec18, sec7, and sec6. Oligosaccharides isolated from chitinase accumulating in cells at the nonpermissive temperature revealed Man1 and Man2 associated with the sec18 mutant. sec6 and sec7 accumulated Man2-Man5 with a higher proportion of Man5 relative to the secreted protein. A significant amount of chitinase is also found associated with the cell wall through binding of COOH-terminal domain to chitin. Disruption of the gene for the enzyme leads to a defect in cell separation but does not substantially alter the level of cellular chitin.