Isolation and molecular characterization of the CaPHO85 gene: a negative regulator of phosphate metabolism (PHO system) in Candida albicans

Abstract

The PHO system is an ingenious mechanism by which the yeast Saccharomyces cerevisiae regulates the expression of a set of genes involved in phosphate metabolism in response to the change of phosphate concentrations in the environment. A key factor in this mechanism is the Pho85 kinase, which has been discovered as a negative regulator of the PHO system. One of the genes isolated in our laboratory in screening the protein kinase genes from Candida albicans was identified as a homologue (CaPHO85) of the PHO85 of S. cerevisiae, based on the following results. a) Pho85 is the polypeptide with the highest homology to CaPho85 (62% identity) among the S. cerevisiae genome sequence. b) The position of insertion of the intron is quite similar between CaPHO85 (in the 7th codon of the N-terminal MTGSSSQ) and S. cerevisiae PHO85 (in the 6th codon of the N-terminal MSSSSQ). c) The nucleotide sequences in the intron possess the consensus sequences for yeast intron: the 5-splice-site, internal, and the 3-splice-site sequence. d) CaPHO85 complemented the S. cerevisiae pho85 mutation. e) CaPho85 contains all of the consensus sequences for the ATP-binding domain and for the kinase domain found in S. cerevisiae Pho85.