Loss of the plasma membrane-bound protein Gas1p in Saccharomyces cerevisiae results in the release of beta1,3-glucan into the medium and induces a compensation mechanism to ensure cell wall integrity.

Deletion of GAS1/GGP1/CWH52 results in a lower beta-glucan content of the cell wall and swollen, more spherical cells (L. Popolo, M. Vai, E. Gatti, S. Porello, P. Bonfante, R. Balestrini, and L. Alberghina, J. Bacteriol. 175:1879-1885, 1993; A. F. J. Ram, S. S. C. Brekelmans, L. J. W. M. Oehlen, and F. M. Klis, FEBS Lett. 358:165-170, 1995). We show here that gas1delta cells release beta1,3-glucan into the medium. Western analysis of the medium proteins with beta1,3-glucan- and beta1,6-glucan-specific antibodies showed further that at least some of the released beta1,3-glucan was linked to protein as part of a beta1,3-glucan-beta1,6-glucan-protein complex. These data indicate that Gas1p might play a role in the retention of beta1,3-glucan and/or beta-glucosylated proteins. Interestingly, the defective incorporation of beta1,3-glucan in the cell wall was accompanied by an increase in chitin and mannan content in the cell wall, an enhanced expression of cell wall protein 1 (Cwp1p), and an increase in beta1,3-glucan synthase activity, probably caused by the induced expression of Fks2p. It is proposed that the cell wall weakening caused by the loss of Gas1p induces a set of compensatory reactions to ensure cell integrity.