Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides. Two genes for this protein are present in M.tuberculosis; this is the active form. When coexpressed in E.coli with nrdE the 2 proteins complement a temperature-sensitive E.coli mutant. [thioredoxin]-disulfide + a 2'-deoxyribonucleoside 5'-diphosphate + H2O = [thioredoxin]-dithiol + a ribonucleoside 5'-diphosphate Binds 2 iron ions per subunit. CDP reduction is stimulated by dATP. Genetic information processing; DNA replication. Tetramer of two alpha and two beta subunits. Initially decreases as oxygen levels drop, then rises again. Lethality. Belongs to the ribonucleoside diphosphate reductase small chain family.