Component of the proteasome core, a large protease complex with broad specificity involved in protein degradation. The M.smegmatis proteasome is able to cleave oligopeptides after hydrophobic residues, thus displaying chymotrypsin-like activity. In complex with the ATPase Mpa, degrades protein targets conjugated to a prokaryotic ubiquitin-like protein (Pup). Among the identified substrates of the M.smegmatis proteasome are the pupylated SodA and Ino1 proteins (PubMed:19028679). The Pup-proteasome system (PPS) is essential for survival under starvation; PPS likely functions to recycle amino acids under nitrogen starvation, thereby enabling the cell to maintain basal metabolic activities (PubMed:24986881). Cleavage of peptide bonds with very broad specificity. The formation of the proteasomal ATPase ARC-20S proteasome complex, likely via the docking of the C-termini of ARC into the intersubunit pockets in the alpha-rings, may trigger opening of the gate for substrate entry. Interconversion between the open-gate and close-gate conformations leads to a dynamic regulation of the 20S proteasome proteolysis activity (By similarity). PPS auto-regulates its own activity via pupylation and degradation of its components (PubMed:24986881). Peptidolytic activity is inhibited by N-acetyl-Leu-Leu-norleucinal (Ac-LLnL) in vitro (PubMed:9282749). Protein degradation; proteasomal Pup-dependent pathway. The 20S proteasome core is composed of 14 alpha and 14 beta subunits that assemble into four stacked heptameric rings, resulting in a barrel-shaped structure. The two inner rings, each composed of seven catalytic beta subunits, are sandwiched by two outer rings, each composed of seven alpha subunits. The catalytic chamber with the active sites is on the inside of the barrel. Has a gated structure, the ends of the cylinder being occluded by the N-termini of the alpha-subunits. Is capped by the proteasome-associated ATPase, ARC. Cells lacking this gene are viable and grow at the wild-type rate, but show a large reduction in the rate of degradation of the pupylated substrates (PubMed:19028679, PubMed:9282749). Cells lacking the Pup-proteasome system (pup/prcS, prcA and prcB) completely lack pupylated proteins and intact proteasomes; they grow as well as wild-type during the exponential phase, but they show reduced survival after prolonged incubation at stationary phase (17 days after inoculation) and become hypersensitive to nitrogen limitation, and, to a lesser extent, to carbon limitation (PubMed:24986881). Belongs to the peptidase T1B family.