CONTROL OF FILAMENT FORMATION IN CANDIDA-ALBICANS BY THE TRANSCRIPTIONAL REPRESSOR TUP1

The pathogenic yeast Candida albicans regulates its cellular morpholog y in response to environmental conditions. Ellipsoidal, single cells ( blastospores) predominate in rich media, whereas filaments composed of elongated cells that are attached end-to-end form in response to star vation, serum, and other conditions. The TUP1 gene, which encodes a ge neral transcriptional repressor in Saccharomyces cerevisiae, was isola ted from C. albicans and disrupted. The resulting tup1 mutant strain o f C. albicans grew exclusively as filaments under all conditions teste d. TUP1 was epistatic to the transcriptional activator CPH1, previousl y found to promote filamentous growth. The results suggest a model whe re TUP1 represses genes responsible for initiating filamentous growth and this repression is lifted under inducing environmental conditions.