CANDIDA-ALBICANS ALS1 - DOMAINS RELATED TO A SACCHAROMYCES-CEREVISIAESEXUAL AGGLUTININ SEPARATED BY A REPEATING MOTIF

Transfer of budding Candida albicans yeast cells from the rich, comple x medium YEPD to the defined tissue culture medium RPMI 1640 (RPMI) at 37 degrees C and 5% CO2 causes rapid onset of hyphal induction. Among the genes induced under these conditions are hyphal-specific genes as well as genes expressed in response to changes in temperature, CO2 an d specific media components. A cDNA library constructed from cells inc ubated for 20 min in RPMI was differentially screened with yeast (YEPD )- and hyphal (RPMI)-specific probes resulting in identification of a gene expressed in response to culture conditions but not regulated by the yeast-hyphal transition. The deduced gene product displays signifi cant identity to Saccharomyces cerevisiae a-agglutinin, encoded by AG alpha 1, an adhesion glycoprotein that mediates mating of haploid cell s. The presence of this gene in C. albicans is curious since the organ ism has not. been observed to undergo meiosis. We designate the C. alb icans gene ALS1 (for agglutinin-like sequence). While the N- and C-ter mini of the predicted 1260-amino-acid ALS1 protein resemble those of t he 650-amino-acid AG alpha 1, ALS1 contains a central domain of tandem repeats consisting of a highly conserved 36-amino-acid sequence not p resent in AG alpha 1. These repeats are also present on the nucleotide level as a highly conserved 108 bp motif. Southern and Northern blot analyses indicate a family of C. albicans genes that contain the tande m repeat motif; at least one gene in addition to ALS1 is expressed und er conditions similar to those for ALS1 expression. Genomic Southern b lots from several C. albicans isolates indicate that the number of cop ies of the tandem repeat element in ALS1 differs across strains and, i n some cases, between ALS1 alleles in the same strain, suggesting a st rain-dependent variability in ALS1 protein size. Potential roles for t he ALS1 protein are discussed.