Identification of a Candida albicans homologue of the PHO85 gene, a negative regulator of the PHO system in Saccharomyces cerevisiae

In a screen for the protein kinase genes of the human pathogenic yeast Candida albicans, a putative homologue (CaPHO85) of PHO85, a negative regulator of the PHO system of Saccharomyces cerevisiae, which is one of the cyclin-dependent protein kinases (CDKs), was isolated. An open reading frame (ORF) of this gene was identified encoding a predicted protein of 326 amino acids with a calculated molecular weight of 37.6 kDa. The amino acid sequence is highly homologous to S. cerevisiae Pho85 (62% identity) and its Aspergillus nidulans homologue (70% identity), but less homologous to Cdc28 (50% identity) of S. cerevisiae and to its C. albicans homologue CaCdc28 (49% identity), both of which are also CDK. The coding region for the C. albicans gene was interrupted by an intron of 81 nucleotides near the sequence encoding the N-terminal region, similarly to the case of the S. cerevisiae PHO85 gene. Alignment of CaPho85 with various yeast CDKs revealed that most of the domains for ATP-binding and protein kinase activity are conserved among fungal species. Southern blot analysis indicated that CaPHO85 is most likely present as a single copy gene. This gene complemented the pho85 mutation of S. cerevisiae by transformation.