ATP-sulfurylaseATP-sulfurylase (ATPS), also known as sulfate adenylate transferase, catalyzes the transfer of an adenylyl group from ATP to sulfate, forming adenosine 5'-phosphosulfate (APS). This reaction is generally accompanied by a further reaction, catalyzed by APS kinase, in which APS is phosphorylated to yield 3'-phospho-APS (PAPS). In some organisms the APS kinase is a separate protein, while in others it is incorporated with ATP sulfurylase in a bifunctional enzyme that catalyzes both reactions. In bifunctional proteins, the domain that performs the kinase activity can be attached at the N-terminal end of the sulfurylase unit or at the C-terminal end, depending on the organism. While the reaction is ubiquitous among organisms, the physiological role of the reaction varies. In some organisms it is used to generate APS from sulfate and ATP, while in others it proceeds in the opposite direction to generate ATP from APS and pyrophosphate. ATP sulfurylase can be a monomer, a homodimer, or a homo-oligomer, depending on the organism. ATPS belongs to a large superfamily of nucleotidyltransferases that includes pantothenate synthetase (PanC), phosphopantetheine adenylyltransferase (PPAT), and the amino-acyl tRNA synthetases. The enzymes of this family are structurally similar and share a dinucleotide-binding domain.