The programs of protein synthesis accompanying the establishment of alternative phenotypes in Candida albicans

Under the regime of pH-regulated dimorphism, stationary phase cells of the dimorphic yeast Candida albicans can be induced to form exclusively and synchronously ellipsoidal buds or elongate mycelia at the same temperature and in the same nutrient medium, the sole determinant of phenotype in this case being pH. Employing pH-regulated dimorphism, cells were pulse-labeled with [35S]-methionine during three consecutive intervals encompassing the preevagination period, the period including evagination and phenotypic commitment, and the post-evagination period. Labeled polypeptides were analyzed by 2D-PAGE. Of the 374 polypeptides examined, the majority (237) did not differ significantly in relative incorporation between the three pulse periods and were similar between budding and mycelium-forming populations. Sixty polypeptides were labeled at negligible or relatively low levels during the first pulse period, but at significantly higher levels during the second and third or third pulse periods. All but one were similar between budding and mycelium-forming populations. Seventeen polypeptides were synthesized at relatively high levels during the first pulse period, but at reduced or negligible levels during the second and third or third pulse periods. All but one were similar between budding and mycelium-forming populations. Only two polypeptides were found to be associated exclusively with mycelium-forming cultures, two associated exclusively with budding cultures, and two enriched significantly in budding cultures of wild-type cells. Employing a variant, MD20, which forms buds at both low and high pH, it was demonstrated that only one mycelium-associated polypeptide and only one bud-associated polypeptide are phenotype rather than pH-specific. Limits to this method of phenotype comparison are outlined, and the unusual similarity rather than dissimilarity in the programs of gene expression between the diverging populations considered in terms of phenotypic regulation.