Loss of the plasma membrane-bound protein Gas1p in Saccharomyces cerevisiae results in the release of β1,3-glucan into the medium and induces a compensation mechanism to ensure cell wall integrity

Deletion of GAS1/CGP1/CWH52 results in a lower beta-glucan content of the cell wall and swollen, more spherical tells (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. fills, FEES Lett. 358:165-170, 1995), We show here that gas1 Delta cells release beta 1,3-glucan into the medium. Western analysis of the medium proteins with beta 1,3-glucan- and beta 1,6-glucan-specific antibodies showed further that at least some of the released beta 1,3-glucan was linked to protein as part of a beta 1,3-glucan-beta 1,6-glucan-protein complex, These data indicate that Gas1p might play a role in the retention of beta 1,3-glucan and/or beta-glucosylated proteins. Interestingly, the defective incorporation of beta 1,3-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 beta 1,3-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.