Nucleoside diphosphate kinases (NMEs) play an important role in the reversible phosphorylation of nuceloside diphosphates (NDP) other than ADP to form nuceloside triphosphates (NTP). The gamma phosphate of ATP is transferred to the beta phosphate on NDP via a ping-pong mechanism, using a phosphorylated active-site intermediate. Nucleoside diphosphate kinase 3 (NME3, aka nm23-H3) can readily form mixed hexamers with NME1, consistent with well-characterised NME family members. The overexpression of the NME3 gene inhibits differentiation and induces the apoptosis of myeloid precursor cell lines (Erent et al. 2001). A putative nucleoside diphosphate kinase (NME2P1) is proposed to perform the same NDPK function as NME1:NME3 heterohexamer based on sequence similarity.