Structure and regulation of the HSP90 gene from the pathogenic fungus Candida albicans

Candida albicans HSP90 sequences were isolated by screening cDNA and genomic libraries with a probe derived from the Saccharomyces cerevisiae homolog, HSP82, which encodes a member of the heat shock protein 90 family of molecular chaperones. Identical sequences were obtained for the 2,197-bp overlap of the cDNA and gene sequences, which were derived from C. albicans 3153A and ATCC 10261, respectively. The C. albicans HSP90 gene contained no introns, and it showed strong homology (61 to 79% identity) to HSP90 sequences from other fungi, vertebrates, and plants. The C-terminal portion of the predicted Hsp90 amino acid sequence was identical to the 47-kDa protein which is thought to be immunoprotective during C. albicans infections (R. C. Matthews, J. Med. Microbiol. 36:367-370, 1992), confirming that this protein represents the C-terminal portion of the 81-kDa Hsp90 protein. Quantitative Northern (RNA) analyses revealed that C. albicans HSP90 mRNA was heat shock inducible and that its levels changed during batch growth, with its maximum levels being reached during the mid-exponential growth phase. HSP90 mRNA levels increased transiently during the yeast-to-hyphal transition but did not correlate directly with germ tube production per se. These data do not exclude a role for Hsp90 in the dimorphic transition. Southern blotting revealed only one HSP90 locus in the diploid C. albicans genome. Repeated attempts to disrupt both alleles and generate a homozygous C. albicans delta hsp90/delta hsp90 null mutant were unsuccessful. These observations suggest the existence of a single HSP90 locus which is essential for viability in C. albicans.