Phase-specific protein expression in the dimorphic yeast Saccharomyces cerevisiae.

In oxygen-limited continuous culture, Saccharomyces cerevisiae formed pseudohyphae by unipolar budding. We developed a continuous cultivation sequence to discriminate phase-specific from metabolically regulated proteins during dimorphism. Computer-aided substractive analysis of 2D-PAGE protein patterns allowed the detection of proteins specifically expressed during yeast and pseudohyphal phases. Image analysis resolved 3 spots that were specific to the pseudohyphal phase and 2 spots that were specific to yeast phase. In addition to phase-specific proteins, important regulation of protein expression took place. A group of 9 proteins was highly over-expressed during the yeast phase when another group of 12 was underexpressed. This phenomenon was reversed during the pseudohyphal phase. These experiments showed that dimorphism in S. cerevisiae is associated with the expression of specific proteins and suggest that yeast phase-specific proteins maintain the yeast form or repress pseudohyphae formation.