A novel vacuolar protein encoded by SSU21/MCD4 is involved in cell wall integrity in yeast

Using a screening procedure for obtaining yeast strains with enhanced abili ty to secrete heterologous protein, we have isolated a mutant with alterati on of the cell wall structure. This mutant displayed strong decrease in cel l wall mannoprotein content, which was not accompanied by decreased glycosy lation of secreted proteins. The mutation defines a gene, designated SSU21 (identical to previously characterized MCD4), which encodes a novel vacuola r protein. SSU21 is probably connected to the cell integrity protein kinase C-mediated pathway, since ssu21 and pkc1 Delta double mutant is synthetic lethal. To our knowledge, this is the first example of a yeast vacuolar pro tein whose alteration results in a cell wall defect. Copyright (C) 1999 Joh n Wiley & Sons, Ltd.