Pyrrolopyrimidine containing metabolites, collectively referred to as deazapurines, comprise a diverse structural group of compounds with varied functions. Deazapurines have been utilized by nature in a broad variety of organisms from bacteria to man. They include compounds with antibacterial and antineoplastic activities as well as redox cofactors involved in DNA repair. Although it is known that deazapurine-containing compounds are derived from purines, the initial steps of deazapurine biosynthesis remain to be elucidated. Two deazapurine nucleoside antibiotics, toyocamycin and sangivamycin, are produced by the soil bacterium Streptomyces rimosus. The nitrile group on toyocamycin is converted to an amide in sangivamycin by an enzyme with nitrile hydrolase activity. We have purified the nitrile hydolase acitivity to near homogeneity revealing at least three associated proteins. N-terminal sequences that have been obtained for each protein are guiding our current efforts toward identifying the genes encoding the enzymes involved in the biosynthesis of these molecules in Streptomyces. This research is supported (in part) by a Career Award in the Biomedical Sciences from the Burroughs Wellcome Fund. Additional support from NIH (GM 72623) is gratefully acknowledged.