Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides. R1 contains the binding sites for both substrates and allosteric effectors and carries out the actual reduction of the ribonucleotide. It also provides redox-active cysteines. [thioredoxin]-disulfide + a 2'-deoxyribonucleoside 5'-diphosphate + H2O = [thioredoxin]-dithiol + a ribonucleoside 5'-diphosphate Under complex allosteric control mediated by deoxynucleoside triphosphates and ATP binding to separate specificity and activation sites on the alpha subunit. The type of nucleotide bound at the specificity site determines substrate preference. It seems probable that ATP makes the enzyme reduce CDP and UDP, dGTP favors ADP reduction and dTTP favors GDP reduction. Stimulated by ATP and inhibited by dATP binding to the activity site. In vitro, its activity is increased by dithiothreitol (DTT) or thioredoxins (non-specific). Inhibited by hydroxyurea, leads to dNTP depletion, replication fork arrest and genomic instability (PubMed:20005847). Genetic information processing; DNA replication. Tetramer of two alpha (R1) and two beta (R2) subunits. The B1 protein is a dimer of alpha subunits. A radical transfer pathway occurs between 'Tyr-122' of R2 and R1. Induced 5-fold by hydroxyurea (at protein level). Binding of the substrate occurs primarily when the active-site cysteines are reduced. E.coli produces two separate class I enzymes. This one is the functional enzyme during growth. Two distinct regulatory sites have been defined: one controls substrate specificity and the other regulates the overall catalytic activity. A substrate-binding catalytic site, located on R1, is formed only in the presence of the second subunit R2. Belongs to the ribonucleoside diphosphate reductase large chain family.