KEX2 INFLUENCES CANDIDA-ALBICANS PROTEINASE SECRETION AND HYPHAL FORMATION

Candida albicans possesses at least seven differentially expressed gen es that encode virulence-related secretory aspartyl proteinases (Saps) , Sap DNA sequences predict post-translational processing at lysine ar ginine residues in the preproteins, reminiscent of the maturation of S accharomyces cerevisiae alpha-factor, where a prepropolypeptide is con verted into a biologically active pheromone by Kex2, a subtilisin-like proprotein convertase. To investigate involvement of a C. albicans KE X2 homologue in Sap activation, a genetic selection was performed base d on KEX2 function, A kex2 strain of S. cerevisiae was transformed wit h a C. albicans genomic DNA library and screened for the production of active alpha-factor. Positive clones were assayed for killer toxin ac tivity, another Kex2-dependent phenotype. Plasmids that rescued both d efects contained a sequence encoding a protein homologous to S. cerevi siae Kex2. Both alleles of the C. albicans REX2 were inactivated by su ccessive mutations, Null mutants continued to secrete active Sap2; how ever, the enzyme was abnormally processed and secreted at reduced leve ls, Unexpectedly, null mutants were incapable of forming hyphae, inste ad differentiating into aberrantly shaped cells. The ability to normal ly process Sap2 and form hyphae was restored upon transformation of nu ll mutants with a KEX2-containing plasmid.