<p>The R2 protein of ribonucleotide reductase catalyses the reduction of all four ribonucleotides to deoxyribonucleotides for use in DNA synthesis. This catalysis involves generating and storing a tyrosyl radical, which is essential for ribonucleotide reduction. The crystal structure consists of a core of four helices in a closed bundle with a left-handed twist and one crossover connection, and a bimetal-ion centre in the middle of the bundle [<cite idref="PUB00016337"/>].</p><p>This entry represents a family of proteins that are structurally related to the R2 protein of class I ribonucleotide reductase, which includes the alpha and beta subunits of methane monooxygenase hydrolase, and delta 9-stearoyl-acyl carrier protein desaturase [<cite idref="PUB00016338"/>].</p>