Isolation and characterization of yeast specific genes from the dimorphic pathogenic fungus Histoplasma capsulatum
Histoplasma capsulatum , a dimorphic pathogenic fungus, is the causative agent of the disease histoplasmosis. This disease has a worldwide occurrence and is endemic in the United States in the Mississippi and Ohio Valleys. In the soil, at approximately 25°C, Histoplasma capsulatum grows as a multicellular saprophytic mold, but in the infected host, at 37°C, it grows as a unicellular yeast. This transition is important in the pathogenicity of the organism. Using a subtractive cDNA library and subtractive hybridization techniques, we isolated two clones which appear to be strongly upregulated in the yeast phase. These clones, Y86AS1.7 and Y86AS2, have been tentatively identified using GENEBANK as encoding a L2 ribosomal protein and a thiol specific antioxidant protein, respectively. Northern blot analysis indicated that the message for the Y86AS1.7 clone produced a primary transcript of 1.3kb which was 7.4 times more abundant in the yeast phase of the organism than the mold phase. The message Y86AS2 was 0.97kb in size and was expressed 15.7 times more in the yeast phase than the mold.