ATPase which is responsible for recognizing, binding, unfolding and translocation of pupylated proteins into the bacterial 20S proteasome core particle. May be essential for opening the gate of the 20S proteasome via an interaction with its C-terminus, thereby allowing substrate entry and access to the site of proteolysis. Thus, the C-termini of the proteasomal ATPase may function like a 'key in a lock' to induce gate opening and therefore regulate proteolysis. ATPase activity is inhibited by N-ethylmaleimide (NEM) but not by sodium azide. Is also able to cleave CTP at half the rate of ATP hydrolysis, but GTP or UTP are not substrates. Optimum pH is 7-8. Protein degradation; proteasomal Pup-dependent pathway. Homohexamer. Assembles into a hexameric ring structure that likely caps the 20S proteasome core. Can form a complex composed of two stacked hexameric rings in vitro. Probably interacts with the prokaryotic ubiquitin-like protein Pup through a hydrophobic interface; the expected interacting region of ARC lies in its N-terminal coiled-coil domain. There is likely one Pup binding site per ARC hexamer ring. Upon ATP-binding, the C-terminus of ARC probably interacts with the alpha-rings of the proteasome core, possibly by binding to the intersubunit pockets. Constitutively expressed. Consists of three main regions, an N-terminal coiled-coil domain (residues 1-77) that probably binds to protein Pup and functions as a docking station, an interdomain (residues 78-227) involved in Mpa hexamerization, and a C-terminal ATPase domain of the AAA type (residues 228-533). Belongs to the AAA ATPase family.