ALS51, a Newly Discovered Gene in the Candida Albicans ALS Family, Created by Intergenic Recombination: Analysis of the Gene and Protein, and Implications for Evolution of Microbial Gene Families

The Candida albicans ALS family has eight genetic loci, each encoding a large glycoprotein. Als protein function is discussed most frequently in terms of adhesion to host and abiotic surfaces. Analyses of C. albicans strain WO-1 indicated variation within the ALS1 locus compared with other isolates such as SC5314. Investigation revealed a recombination between the contiguous ALS5 and ALS1 loci to generate a new coding region, named ALS51, because it encodes the 5' domain of ALS5 fused in-frame to the tandem repeat region and 3' domain of ALS1. ALS51 was detected in 11 isolates (4.6%) from a collection of 239 C. albicans strains of diverse origin and clade assignment. The 12 ALS51-positive strains identified in this study represented three different ALS family genotypes with respect to the presence and copy number of ALS51, ALS5 and ALS1. ALS51 transcription was detected by real-time reverse-transcription-PCR in WO-1. Although the cell-surface abundance of Als51 on WO-1 and Als5 on SC5314 was too low to visualize by indirect immunofluorescence using an anti-Als5 monoclonal antibody, both proteins were observed on Western blots of β-1,6-glucanase-digested C. albicans cell walls. Characterization of ALS51 illustrates one of the recombination mechanisms that generate diversity within C. albicans gene families.