Harnessing free radicals: formation and function of the tyrosyl radical inribonucleotide reductase

Ribonucleotide reductases (RNRs) are uniquely responsible for converting nu cleotides to deoxynucleotides in all organisms. The cofactor of class-I RNR s comprises a di-iron cluster and a tyrosyl radical, and is essential for i nitiation of radical-dependent nucleotide reduction. Recently, much progres s has been made in understanding the mechanism by which this cofactor is ge nerated in vitro and in vivo, as well as the function of the tyrosyl radica l in nucleotide reduction. The Escherichia coli RNR cofactor provides a par adigm for cofactors in other di-iron requiring or tyrosyl-radical-requiring proteins.