Sed1p and Srl1p are required to compensate for cell wall instability in Saccharomyces cerevisiae mutants defective in multiple GPI‐anchored mannoproteins

Abstract

The covalently linked cell wall protein Ccw12p of Saccharomyces cerevisiae is a GPI-anchored protein (V. Mrsa et al., 1999, J Bacteriol 181: 3076–3086). Although only 121 amino acids long, the haemagglutinin-tagged protein released by laminarinase from the cell wall possesses an apparent molecular mass of > 300 kDa. A membrane-bound form with an apparent molecular mass of 58 kDa is highly O- and N-glycosylated and contains the GPI anchor. With a half-life of 2 min, the membrane form is transformed to the > 300 kDa form. The deletion mutant ccw12Δ grows slower than the wild type, is highly sensitive to Calcofluor white and contains 2.5 times more chitin. Further, compared with wild-type yeast, significantly more proteins are released from intact cells when treated with dithiothreitol. Interestingly, these defects become less pronounced when further GPI-anchored cell wall proteins are deleted. Mutant ΔGPI (simultaneous deletion of CCW12, CCW13/DAN1, CCW14, TIP1 and CWP1) is similar in many respects to wild-type yeast. To find out how the cell wall is stabilized in mutant ΔGPI, a genome-wide transcription analysis was performed. Of 159 significantly regulated genes, 14 encode either known or suspected cell wall-associated proteins. Analysis of genes affected in transcription revealed that SED1 and SRL1 in particular are required to reconstruct cell wall stability in the absence of multiple GPI-anchored mannoproteins.