GENETIC-ANALYSIS OF REGULATORY MUTANTS AFFECTING SYNTHESIS OF EXTRACELLULAR PROTEINASES IN THE YEAST YARROWIA-LIPOLYTICA - IDENTIFICATION OF A RIM101 PACC HOMOLOG/

Depending on the pH of the growth medium, the yeast Yarrowia lipolytic a secretes both an acidic proteinase and an alkaline proteinase, the s ynthesis of which Is also controlled by carbon, nitrogen, and sulfur a vailability, as well as by the presence of extracellular proteins. Rec essive mutations at four unlinked loci, named PAL1 to PAL4, mere isola ted which prevent alkaline proteinase derepression under conditions of carbon and nitrogen limitation at pH 6.8, These mutations markedly af fect mating and sporulation, A dominant suppressor of all four PAL mut ations was isolated from a wild-type genomic library, which turned out to be a C-terminally truncated form of a 585-residue transcriptional factor of the His(2)Cys(2) zinc finger family, which we propose to cal l YIRim101p, Another C-terminally truncated version of YIRim101p (419 residues) is encoded by the dominant RPH2 mutation previously isolated as expressing alkaline protease independently of the pH. YIRim101p is homologous to the transcriptional activators Rim101p of Saccharomyces cerevisiae, required for entry into meiosis, and PacC of Aspergillus nidulans and Penicillium chrysogenum, which were recently shown to med iate regulation by ambient pH. YIRim101p appears essential for mating and sporulation and for alkaline proteinase derepression, YIRIM101 exp ression is autoregulated, maximal at alkaline pH, and strongly impaire d by PAL mutations.