Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides (By similarity). Inhibits Wnt signaling (By similarity). [thioredoxin]-disulfide + a 2'-deoxyribonucleoside 5'-diphosphate + H2O = [thioredoxin]-dithiol + a ribonucleoside 5'-diphosphate Binds 2 iron ions per subunit. Genetic information processing; DNA replication. Heterodimer of a large and a small subunit. Interacts (via Cy motif and when phosphorylated at Thr-33) with CCNF; the interaction occurs exclusively in G2 and early M (By similarity). Localized to the cytoplasm in S phase cells. May localize to the nucleus in G2 phase cells. Phosphorylation on Ser-20 relieves the inhibitory effect on Wnt signaling (By similarity). Phosphorylated on Thr-33 by CDK1 and CDK2; predominantly in G2 and M phase (By similarity). Ubiquitinated by the SCF(CCNF) E3 ubiquitin-protein ligase complex; leading to its degradation by the proteasome. 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 M1, is formed only in the presence of the second subunit M2. Belongs to the ribonucleoside diphosphate reductase small chain family.