Structures of the Yeast Ribonucleotide Reductase Rnr2 and Rnr4 Homodimers

Ribonucleotide reductases (RNRs) catalyze the reduction of ribonucleotides to the corresponding deoxyribonucleotides using free-radical chemistry. These enzymes are responsible for maintaining proper levels of DNA precursors for replication and repair and therefore play a crucial role in all organisms. RNRs are divided into three classes based o­n the nature of the catalytically essential radical. Class I RNRs, found in mammals, plants, yeast, DNA viruses, and Escherichia coli, consist of two dimeric subunits called R1 and R2. The R1 subunit contains binding sites for substrate and allosteric effectors, and the R2 subunit houses a diiron-tyrosyl radical cofactor.

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