This model represents the alpha (large) chain of the class I ribonucleotide reductase (RNR). RNR's are responsible for the conversion of the ribose sugar of RNA into the deoxyribose sugar of DNA. This is the rate-limiting step of DNA biosynthesis. Class I RNR's generate the required radical (on tyrosine) via a "non-heme" iron cofactor which resides in the beta (small) subunit. The alpha subunit contains the catalytic and allosteric regulatory sites. The mechanism of this enzyme requires molecular oxygen. E. Coli contains two versions of this enzyme which are regulated independently (NrdAB and NrdEF, where NrdA and NrdE are the large chains). Most organisms contain only one, but the application of the gene symbols NrdA and NrdE are somewhat arbitrary. This model identifies RNR's in diverse clades of bacteria, eukaryotes as well as numerous DNA viruses and phage. [Purines, pyrimidines, nucleosides, and nucleotides, 2'-Deoxyribonucleotide metabolism]
Jiyao W et al.(2023). "The conserved domain database in 2023.",