The evolution of ribonucleotide reduction revisited

Ribonucleotide reductases (RNRs) catalyze the conversion of both purine and pyrimidine nucleotides to deoxynucleotides in all organisms and provide al l the monomeric precursors essential for both DNA replication and repair. R NRs have been divided into three classes on the basis of their unique metal lo-cofactors. The exquisitely controlled free radical chemistry used by all RNRs, and the commonality of the structures of the subunits where the nucl eotide reduction process occurs, together provide compelling evidence for t he importance of chemistry in the divergent evolution of RNRs from a common progenitor.