Catalyzes the conversion of ribonucleotides into deoxyribonucleotides, which are required for DNA synthesis and repair. a ribonucleoside 5'-triphosphate + formate + H(+) = a 2'-deoxyribonucleoside 5'-triphosphate + CO2 + H2O Activated under anaerobic conditions by NrdG, a tightly associated activase. Activation involves the formation of a glycyl radical at Gly-580. Homodimer. Forms a tetramer composed of two NrdD and two NrdG subunits. Belongs to the anaerobic ribonucleoside-triphosphate reductase family.