Determination of the Stability of Protein Pools from the Cell Wall of Fungi

Stability of the protein populations present in the cell wall of three ascomycetous fungi Candida albicans, Saccharomyces cerevisiae and Yarrowia lipolytica was investigated. Cell wall proteins were either labeled with biotin or radiolabeled with amino acids, and chased for a period of time representing several generations. Proteins linked by non-covalent or covalent bonds were separated and their turnover was analyzed. No significant turnover took place during the chase period, and in fact radioactive proteins were accumulated in the wall during the period possibly by transfer through the secretory pathway. This transfer did not involve de novo protein synthesis; it was inhibited by azide, and by incubation of a sec1 mutant of S. cerevisiae at the non-permissive temperature. It is concluded that proteins bound to the cell wall are stable and that there is no precursor-product relationship among those linked by non-covalent bonds and the covalently bound ones.