Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides. RNR2 provides the diiron-tyrosyl radical center. [thioredoxin]-disulfide + a 2'-deoxyribonucleoside 5'-diphosphate + H2O = [thioredoxin]-dithiol + a ribonucleoside 5'-diphosphate Binds 2 iron ions per subunit. Optimum temperature is 30 degrees Celsius. 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. Interacts with DIF1. Found predominantly in the nucleus under normal growth conditions and is redistributed to the cytoplasm in damaged cells in a DNA replication and damage checkpoint-dependent manner. Nuclear localization is mediated by DIF1. Induced by DNA-damage. Present with 538 molecules/cell in log phase SD medium. Belongs to the ribonucleoside diphosphate reductase small chain family.