Broad-specificity nucleoside monophosphate (NMP) kinase that catalyzes the reversible transfer of the terminal phosphate group between nucleoside triphosphates and monophosphates. 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 Monomer and homodimer. 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. 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.