Provides the precursors necessary for DNA synthesis. Catalyzes the biosynthesis of deoxyribonucleotides from the corresponding ribonucleotides. R2F contains the tyrosyl radical required for catalysis. [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. Belongs to the ribonucleoside diphosphate reductase small chain family.