PROJECT SUMMARY Biosynthetic pathways are rich in enzymatic transformations that produce structurally diverse natural products, such as secondary metabolites, modified nucleic acids, and modified peptides. Discovering and understanding the molecular basis for these transformations underpins efforts towards development of deep insights into factors that either belie many disease processes, or their use in development of therapeutic agents. The two major NIGMS-funded research areas in the Bandarian lab at the University of Utah focus on (1) discovering the molecular basis of biogenesis of the pyrrolopyrimidine core structure found in a variety of secondary metabolites, as well as in the hypermodified base, queuosine, and (2) elucidating the mechanism of enzymes involved in the biosynthetic pathways of ribosomally synthesized posttranscriptionally modified polypeptides (RiPPs), which are emerging as a new group of natural products with substantial potential as therapeutic agents. These pathways often utilize complex radical- mediated enzymatic transformations whose mechanisms are not known. The discovery and mechanistic studies of these enzymes are proposed as part of this R35 application. !