Major role in the synthesis of nucleoside triphosphates other than ATP. The ATP gamma phosphate is transferred to the NDP beta phosphate via a ping-pong mechanism, using a phosphorylated active-site intermediate (PubMed:5793714). Required for repair of UV radiation- and etoposide-induced DNA damage (PubMed:18983998). a 2'-deoxyribonucleoside 5'-diphosphate + ATP = a 2'-deoxyribonucleoside 5'-triphosphate + ADP a ribonucleoside 5'-diphosphate + ATP = a ribonucleoside 5'-triphosphate + ADP Homohexamer and homotetramer. Interacts with TOM40 preferentially in an unfolded, unphosphorylated form. Localizes predominantly to the cytoplasm. A small fraction is present in the mitochondrial intermembrane space. The N-terminus is blocked. Present with 7130 molecules/cell in log phase SD medium. Belongs to the NDK family.