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. Protein degradation; proteasomal Pup-dependent pathway. Homohexamer. Assembles into a hexameric ring structure that caps the 20S proteasome core. Strongly interacts with the prokaryotic ubiquitin-like protein Pup through a hydrophobic interface; the interacting region of ARC lies in its N-terminal coiled-coil domain. There is one Pup binding site per ARC hexamer ring. Upon ATP-binding, the C-terminus of ARC interacts with the alpha-rings of the proteasome core, possibly by binding to the intersubunit pockets. Consists of three main regions, an N-terminal coiled-coil domain that binds to protein Pup and functions as a docking station, an interdomain involved in ARC hexamerization, and a C-terminal ATPase domain of the AAA type. Belongs to the AAA ATPase family. Extended N-terminus.