Broad-specificity nucleoside monophosphate (NMP) kinase that catalyzes the reversible transfer of the terminal phosphate group between nucleoside triphosphates and monophosphates. AMP and dAMP are the preferred substrates, but CMP and dCMP are also good substrates. IMP is phosphorylated to a much lesser extent. All nucleoside triphosphates ATP, GTP, UTP, CTP, dATP, dCTP, dGTP, and TTP are accepted as phosphate donors. CTP is the best phosphate donor, followed by UTP, ATP, GTP and dCTP. May have a role in nuclear energy homeostasis. Has also ATPase activity. May be involved in regulation of Cajal body (CB) formation. AMP + ATP = 2 ADP kcat is 6.3 sec(-1) for adenylate kinase activity. kcat is 4.8 sec(-1) for ATPase activity. Monomer and homodimer (By similarity). Interacts with COIL (via C-terminus). Displays widespread diffuse nucleoplasmic distribution but not detected in nucleoli. Detected in Cajal bodies but not in all cells. Expressed in heart, brain, placenta, lung, liver, skeletal muscle, kidney, pancreas, chorionic villi and the central nervous system. Belongs to the adenylate kinase family. AK6 subfamily. AK6 and TAF9 were initially considered as products of the same gene since they share two exons. However, they are translated from different initiation codons and reading frames and encode unrelated proteins. This arrangement is conserved in some mammalian species.