ISOLATION OF THE CANDIDA-ALBICANS HOMOLOGS OF SACCHAROMYCES-CEREVISIAE KRE6 AND SKN1 - EXPRESSION AND PHYSIOLOGICAL-FUNCTION

Cell wall beta-glucan in a pathogenic fungus, Candida albicans, is hig hly branched with beta-1,3 and beta-1,6 linkages. We have isolated the C. albicans cDNAs for KRE6 and SKN1, the genes required for beta-1,6- glucan synthesis in Saccharomyces cerevisiae. The results of Northern blot analysis revealed that C. albicans KRE6 was expressed at a higher level than SKN1 in the yeast phase, while SKN1 expression was strongl y induced upon induction of hyphal formation. In addition, the C. albi cans KRE6 and SKN1 mRNAs but not the actin mRNA were shortened during the yeast-hypha transition. Unlike S. cerevisiae, more than 50% of cel l wall glucan was beta-1,6 linked in C. albicans. Neither beta-1,3-glu can nor beta-1,6-glucan was affected by the homozygous C. albicans skn 1 Delta null mutation. Although we never succeeded in generating the h omozygous C. albicans kre6 Delta null mutant, the hemizygous kre6 Delt a mutation decreased the KRE6 mRNA level by about 60% and also caused a more than 80% reduction of beta-1,6-glucan without affecting beta-1, 3-glucan. The physiological function of KRE6 was further examined by s tudying gene regulation in C. albicans. When KRE6 transcription was su ppressed by using the HEX1 promoter, C. albicans cells exhibited the p artial defect in cell separation and increased susceptibility to Calco fluor White. These results demonstrate that KRE6 plays important roles in beta-1,6-glucan synthesis and budding in C. albicans.