Nearly all organisms depend on the action of a ribonucleotide reductase (RNR) to provide the substrates for DNA replication and repair. This central function offers potential for the development of new RNR inhibitors that could serve as potent antibiotics. All class I RNRs share a common nucleotide reduction mechanism, initiated in the catalytic (alpha) subunit by a cysteine thiyl radical that abstracts an H-atom from the substrate. Class I RNRs use diverse inorganic chemistry in a separate beta subunit to generate the thiyl radical transiently on each turnover. My research group seeks to understand the scope of diversity in class I RNR metallocofactor compositions, structures, and assembly mechanisms, with the eventual goal of targeted inhibition of these pathways in bacterial pathogens. We focus on discovery and characterization of new enzyme subclasses with the objective of gaining more detailed understanding of both cofactor assembly mechanisms and the roles of subclass-specific structural features.