The main objective of this proposal is to characterize the C. albicans ALS gene family and test the hypothesis that the ALS proteins are involved in C. albicans adhesion. The first ALS gene, ALS1 was identified in a differential hybridization screen. The predicted ALS1 protein shares significant identity with the Saccharomyces cerevisiae cell-surface adhesion glycoprotein alpha-agglutinin (AGalpha1). Predicted structural features of ALS1 suggest that it too will be localized on the cell surface, be highly glycosylated and may function in adhesion. ALS1 contains a central domain of tandemly repeated sequence not present in AGalpha1. Southern blots indicated this sequence hybridizes to several C. albicans genomic fragments; all of these are considered to belong to the ALS gene family. This repeated sequence has features suggesting it will be highly N- and O- glycosylated. Proteins modified to this extent will most likely be localized on the cell surface suggesting all ALS proteins have the potential to function in adhesive roles. The basic approach used in these studies involves cloning all ALS genes and completing the DNA sequence of each. These sequences will be compared and regions specific for each ALS gene identified. These specific probes will be used to study the sample strain variability of the ALS genes and define conditions under which the genes are expressed. Unique sequences will also be used to raise antisera specific for ALS proteins. Localization and modification data will be compared between what is observed in C. albicans and what is observed when ALS genes are heterologously expressed in S. cerevisiae. Assuming similar data for each, these S. cerevisiae strains will be assayed to determine if ALS proteins have adhesive properties. The large degree of variability in size and numbers of ALS genes between C. albicans strains may be the first example of a genetic explanation for strain-dependent cell-surface variation in C. albicans. Data derived from studies of the ALS family will also further define the similarities and differences in signals for protein localization and modification between C. albicans and S. cerevisiae. These data will indicate circumstances under which S. cerevisiae, with its well-developed genetic system, can be used to facilitate analyses that would otherwise be complicated in the diploid, asexual C. albicans.
