Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides (By similarity). Two genes for this protein are present in M.tuberculosis; this is thought to not be the active form. When coexpressed in E.coli with nrdE the 2 proteins do not complement a temperature-sensitive E.coli mutant, whereas the other gene (nrdF2) does complement. [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. Tetramer of two alpha and two beta subunits. Expressed in growing cells (at protein level). Transcription not induced under oxygen-limiting conditions. Belongs to the ribonucleoside diphosphate reductase small chain family.