MOLECULAR-CLONING AND SEQUENCE-ANALYSIS OF YPS-3, A YEAST-PHASE-SPECIFIC GENE IN THE DIMORPHIC FUNGAL PATHOGEN HISTOPLASMA-CAPSULATUM

Genes specifically expressed in the parasitic yeast phase of Histoplas ma capsulatum have been cloned to clarify the mechanisms underlying bo th pathogenesis and morphogenesis in this human dimorphic fungal patho gen. Previous studies have determined that the yeast-phase-specific ge ne, yps-3, is expressed differentially in two non-isogenic strains whi ch differ in their thermotolerance and virulence. We have cloned the y ps-3 homologues from the high virulence (G217B) and low virulence (Dow ns) strains, and obtained a partial cDNA clone representing the expres sed gene from H. capsulatum G217B. The Downs clone harbours a 287 bp i nsertion sequence that disrupts a long ORF defined by the yps-3 G217B cDNA. Although the insertion sequence contains features reminiscent of mobile genetic elements, including 15 bp direct repeats of flanking s equence, it is not randomly distributed in the H. capsulatum genome. S 1 nuclease analysis was utilized to map the 5' end of the expressed yp s-3 gene in G217B to potential regulatory regions which are largely ho mologous in both strains. This finding may point to a deficiency in a temperature inducible regulatory protein in the low virulence, tempera ture-sensitive Downs strain. The nucleotide sequence of the yps-3 gene and the predicted amino acid sequence of its product represents the f irst report of phase-specific gene and protein sequences in this widel y distributed fungal pathogen. Further analysis of the product encoded by the yps-3 gene may provide significant insight into the pathogenic repertoire of H. capsulatum.