THE GLUCANASE-SOLUBLE MANNOPROTEINS LIMIT CELL-WALL POROSITY IN SACCHAROMYCES-CEREVISIAE

The cell porosity of batch‐grown Saccharomyces cerevisiae was maximal in the early exponential phase and fell off rapidly to lower levels in later growth phases. Treatment of stationary‐phase cells with alpha‐mannosidase restored wall porosity to the level of cells in early exponential phase. When cells in the early exponential phase were treated with alpha‐mannosidase, or tunicamycin, an inhibitor of N‐glycosylation, even higher porosities were obtained. Mutants with truncated mannan side‐chains in their wall proteins also had very porous walls. The importance of the mannan side‐chains for wall porosity was also seen during sexual induction. Treatment with alpha pheromone, which leads to the formation of wall proteins with shorter mannan side‐chains, enhanced wall porosity. Disulphide bridges also affect cell wall porosity. They were predominantly found in the glucanase‐soluble wall proteins. Because the main part of the mannan side‐chains is also found in this family of wall proteins, our results demonstrate that the glucanase‐soluble mannoproteins limit cell wall porosity in yeast. Copyright © 1990 John Wiley & Sons Ltd.