NONFILAMENTOUS CANDIDA-ALBICANS MUTANTS ARE AVIRULENT

Candida albicans and Saccharomyces cerevisiae switch from a yeast to a filamentous form. In Saccharomyces, this switch is controlled by two regulatory proteins, Ste12p and Phd1p. Single-mutant strains, ste 12/s te12 or phd1/phd1, are partially defective, whereas the sfe12/ste12 ph d1/phd1 double mutant is completely defective in filamentous growth an d is noninvasive. The equivalent cph1/cph1 efg1/efg1 double mutant in Candida (Cph1p is the Ste12p homolog and Efg1p is the Phd1p homolog) i s also defective in filamentous growth, unable to form hyphae or pseud ohyphae in response to many stimuli, including serum or macrophages. T his Candida cph1/cph1 efg1/efg1 double mutant, locked in the yeast for m, is avirulent in a mouse model.