SUMMARY: Saccharomyces cerewisiae and the pathogen Candida albicans can be induced to undergo morphogenesis from a yeast to a filamentous form. A C. albicansgene (CaCCT8) was identified encoding a subunit of the Cct chaperonin complex, whose expression prevents filament formation in both fungi without interfering with growth of the yeast form. In 5. cerewisiae, pseudohyphal growth induced by Ra2 119va, by overproduction of Phdlp or by expression of the C. albicans EFGl gene, was blocked by CaCct8p and its N-terminally deleted derivative CaCct8-Alp; in contrast, pseudohyphal induction by othe components (Cphlp, Cdc42p) could not be suppressed, indicating that morphogenesis per se is not inhibited. CaCCT8 expression also interfered with other Ra2p va119, phenotypes, including heat sensitivity, lack of glycogen accumulation and lack of sporulation. In C. albicans, overproduction of CaCct8p effectively blocked hyphal morphogenesis induced by starvation conditions and by serum. The results suggest that the activity of a component in the Ras2p signal transduction pathway is suppressed by excess chaperonin subunits. This component may be a novel folding target for the Cct complex. In agreement with this hypothesis, disruption of one of the two CaCC7′8 alleles in C. albicans led t o defective hyphal morphogenesis.


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