A 368-Base-Pair cis -Acting HWP1 Promoter Region, HCR, of Candida albicans Confers Hypha-Specific Gene Regulation and Binds Architectural Transcription Factors Nhp6 and Gcf1p

To elucidate the molecular mechanisms controlling the expression of the hypha-specific adhesin geneHWP1 ofCandida albicans , its promoter was dissected and analyzed using a green fluorescent protein reporter gene. A 368-bp region, theHWP1 control region (HCR), was critical for activation under hypha-inducing conditions and conferred developmental regulation to a heterologousENO1 promoter. A more distal region of the promoter served to amplify the level of promoter activation. Using gel mobility shift assays, a 249-bp subregion of HCR, HCRa, was found to bind at least four proteins from crude extracts of yeasts and hyphae with differing binding patterns dependent on cell morphology. Four proteins with DNA binding activities were identified by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis after separation by anion-exchange and heparin-Sepharose chromatography. One protein with high similarity to Nhp6, an HMG1 family member inSaccharomyces cerevisiae , and another with weak similarity to an HMG-like condensation factor fromPhysarum polycephalum implicated changes in chromatin structure as a critical process in hypha-specific gene regulation. Proteins with strong homology to histones were also found. These studies are the first to identify proteins that bind to a DNA segment that confers developmental gene regulation inC. albicans and suggest a new model for hypha-specific gene regulation.