Candida albicans ALS1: domains related to a Saccharomyces cerevisiae sexual agglutinin separated by a repeating motif

Transfer of budding Candida albicans yeast cells from the rich, complex medium YEPD to the defined tissue culture medium RPMl 1640 (RPMI) at 37°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 and specific media components. A cDNA library constructed from cells incubated for 20 min in RPMI was differentially screened with yeast (YEPD)- and hyphal (RPMI)-specific probes resuming in identification of a gene expressed in response to culture conditions but not regulated by the yeast-hyphal transition. The deduced gene product displays significant identity to Saccharomyces cerevisiaeα-agglutinin, encoded by AGα1, an adhesion glycoprotein that mediates mating of haploid cells. The presence of this gene in C albicans is curious since the organism has not been observed to undergo meiosis. We designate the C. albicans gene ALS1 (for a gglutinin-l ike s equence). While the N- and C-termini of the predicted 1260-amino-acid ALS1 protein resemble those of the 650-amino-acid AGα1, ALS1 contains a central domain of tandem repeats consisting of a highly conserved 36-amino-acid sequence not present in AGb1. These repeats are also present on the nucleotide level as a highly conserved 108bp motif. Southern and Northern blot analyses indicate a family of C. albicans genes that contain the tandem repeat motif; at least one gene in addition to ALS1 is expressed under conditions similar to those for ALS1 expression. Genomic Southern blots from several C. albicans isolates indicate that the number of copies of the tandem repeat element in ALS1 differs across strains and. In some cases, between ALS1 alleles in the same strain, suggesting a strain-dependent variability in ALS1 protein size. Potential roles for the ALS1 protein are discussed.