Candida albicans is a commensal yeast which causes infections on the mucosal surfaces of the oral, vaginal and gastrointestinal tracts of humans. Candidiasis can also become invasive, causing systemic infections. Candida infections are particularly prevalent in the AIDS or immunocompromised cancer and transplant patients, and patients using long-term antibacterial antibiotics. Adherence of C. albicans to host cells is a complex process which involves factors such as the type of candida adhesins, nutritional influences, pH, and the type of host cell ligands. Most observations of adherence in Candida involve in vitro studies using either acrylics or human cells. In vivo studies are now possible in which single gene deleted strains can be evaluated for virulence functions. Previous studies have found that C. albicans was more adherent to human esophageal cell lines (HET1-A), human buccal epithelial cells (HEBEC), and a murine alveolar macrophage cell line (MH-S) when grown on media containing 500 mMD-galactose than when grown on 500 mMD- glucose. Additionally, an SDS-PAGE extracted cell wall 190KD mannoprotein (MP 190) was more likely expressed when C. albicans were grown in 500 mMD-glucose than in 500 mMD-glucose The gene encoding this mannoprotein has been identified as a glucoamylse (GCA1) which encodes a protein containing 946 amino acids. It's expression is greater in cells grown in galactose, starch, cellobiose and sucrose, but is minimally expressed in glucose. Expression in a rat model of oral candidiasis also was observed using RT-PCR, indicating that GCA1 is associated with disease development. The specific aims of the proposal are to: 1. Construct strains of C. albicans deleted in GCA1 (construction of the deltagca1). 2 (a). Examine the role of GCA1 in vitro. and (b). Examine the role of GCA1 in vivo (virulence studies). 3. Characterization of Gca1p enzymatically (glucoamylase assays). Our broad objective is to determine the function and role of GCA1 in the growth, morphogenesis, adherence, and virulence of the organism.