Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides. [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 large 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 (By similarity). Genetic information processing; DNA replication. Heterotetramer of two large (R1) and two small (R2) subunits. S.cerevisiae has two different R1 subunits (RNR1 and RNR3) and two different R2 subunits (RNR2 and RNR4). The functional form of the small subunits is a RNR2-RNR4 heterodimer, where RNR2 provides the iron-radical center and RNR4 is required for proper folding of RNR2 and assembly with the large subunits. Under normal growth conditions, the active form of the large subunits is a homodimer of the constitutively expressed RNR1. In damaged cells or cells arrested for DNA synthesis, the reductase consists of multiple species because of the association of the small subunits (RNR2-RNR4) with either the RNR1 homodimer or a heterodimer of RNR1 and the damage-inducible RNR3. Highly induced by DNA-damage. Two distinct regulatory sites have been defined: the specificity site, which controls substrate specificity, and the activity site which regulates overall catalytic activity. A substrate-binding catalytic site, located on R1, is formed only in the presence of the second subunit R2 (By similarity). Present with 1364 molecules/cell in log phase SD medium. Belongs to the ribonucleoside diphosphate reductase large chain family.