With CysD forms the ATP sulfurylase (ATPS) that catalyzes the adenylation of sulfate producing adenosine 5'-phosphosulfate (APS) and diphosphate, the first enzymatic step in sulfur assimilation pathway. APS synthesis involves the formation of a high-energy phosphoric-sulfuric acid anhydride bond driven by GTP hydrolysis by CysN coupled to ATP hydrolysis by CysD. APS kinase catalyzes the synthesis of activated sulfate. ATP + H(+) + sulfate = adenosine 5'-phosphosulfate + diphosphate adenosine 5'-phosphosulfate + ATP = 3'-phosphoadenylyl sulfate + ADP + H(+) Sulfur metabolism; hydrogen sulfide biosynthesis; sulfite from sulfate: step 1/3. Sulfur metabolism; hydrogen sulfide biosynthesis; sulfite from sulfate: step 2/3. Heterodimer composed of CysD, the smaller subunit, and CysNC. In the C-terminal section; belongs to the APS kinase family. In the N-terminal section; belongs to the TRAFAC class translation factor GTPase superfamily. Classic translation factor GTPase family. CysN/NodQ subfamily. It is not obvious if the APS kinase domain is functional; the conserved active site serine (position 546) is replaced by an alanine. Furthermore P.aeruginosa seems to harbor a bona fide single domain APS kinase (CysC).