Isolation and analysis of the unique mold specific gene M46 and the yeast specific gene Y56 from the pathogenic fungus Histoplasma capsulatum
The dimorphic fungus Histoplasma capsulatum , is the etiologic agent of the respiratory disease histoplasmosis, which infects an estimated 500,000 people each year in the United States. The organism grows in the soil (or in the lab at 25°C) as saprophytic multicellular mold form and converts to pathogenic unicellular yeast form in the infected host (or in the lab at 37°C). In the attempt to understand the mechanism of phase conversion, genes specific to the yeast and mold phase are being isolated in our lab. Two such genes M46 specific to the mold phase and Y56 upregulated in the yeast phase were isolated from subtracted cDNA library, prepared with a PCR based normalizing method, which enriches for rare sequences. Northern blot expression studies showed M46 present in mold phase cells but undetectable in yeast phase cells, Y56 was upregulated in the yeast phase cells. Sequence and blast analysis of M46 clone showed no significant homology to any gene in the GenBank. However Y56 showed homology to a recombinant antigen which has been proposed for an antibody-based diagnostic tool for histoplasmosis. Northern blot analysis of M46 gene is four strains of Hc revealed that M46 was expressed in two strains G186AS and Downs but was not expressed in G217B and G184AS strains. Analysis of genomic sequence of M46 from all the strains did not reveal any major sequence changes which could have led to the difference in expression. Y56 was found to be expressed in all strains. Expression of Y56 during Y [arrow right] M transition revealed that Y56 was developmentally regulated.