Candida albicans ALS3 and insights into the nature of the ALS gene family

Abstract

The ALS1 (agglutinin-like sequence) gene of Candida albicans encodes a protein similar to alpha-agglutinin, a cell-surface adhesion glycoprotein of Saccharomyces cerevisiae. A central domain of a tandemly repeated 108-bp sequence is found in the ALS1 coding region. This tandem-repeat motif hybridizes to multiple C. albicans genomic DNA fragments, indicating the possibility of other ALS1-like genes in C. albicans. To determine if these fragments constitute a gene family, tandem-repeat-hybridizing genomic fragments were isolated from a fosmid library by PCR screening using primers based on the consensus tandem-repeat sequence of ALS1. One group of fosmids, designated ALS3, encodes a gene with 81% identity to ALS1. The sequences of ALS1 and ALS3 are most conserved in the tandem-repeat domain and in the region 5' of the tandem repeats. Northern-blot analysis using unique probes from the 3' end of each gene demonstrated that ALS1 expression varies, depending on which C. albicans strain is examined, and that ALS3 is hyphal-specific. Both genes are found in a variety of C. albicans and C. stellatoidea strains examined. The predicted Als1p and Als3p exhibit features suggesting that both are cell-surface glycoproteins. Southern blots probed with conserved sequences from the region 5' of the tandem repeats suggest that other ALS-like sequences are present in the C. albicans genome and that the ALS family may be larger than originally estimated.