The goal of this project is to characterize the physical and certain biological properties of ribosomes of the fungus Histoplasma capsulatum. The biochemical makeup of ribosomes from the yeast and mycelial phases of growth of H. capsulatum will be compared. This will include comparisons of RNA-protein ratios, protein compositions of 60S and 40S ribosomal subunits, as well as ribosomal RNAs. The ribosomes of this organism can be used as a vaccine to protect animals from infection by the homologous organism. Another part of this project will attempt to define the immunogenic factor on the ribosomes. The plan is to extract and purify the ribosomes from this organism under carefully controlled chemical conditions and analyze the protein and RNA as well as any molecules of nonribosomal origin that contaminate ribosome preparations to determine which contain immunogenic activity. The specific component(s) that give immunity will then be chemically purified. We hope that the purified component can be used as a test antigen in later studies to determine the role of humoral or cellular immunity in the acquisition of immunity.