Phenotype analysis of Saccharomyces cerevisiae mutants with deletions in Pir cell wall glycoproteins.

Proteins with internal repeats (Pir) belong to a minor group of covalently linked yeast cell wall proteins. They are not essential for viability but important for cell wall strength, reduced permeability against plant antifungal enzymes and maintenance of osmotic stability. Here we show the importance of Pir proteins of Saccharomyces cerevisiae for growth at low pH and in presence of various inhibitors. Cell wall analysis of Deltapir1,2,3,4 deletion strain revealed slightly increased chitin content and changes in relative proportion of alkali-soluble and insoluble glucan and chitin fractions. Activation of the cell wall integrity pathway was indicated by increased levels of double phosphorylated Mpk1p/Slt2p in the pir deletants.