Vacuolar proteinase B involved in protein degradation in the vacuole. Among other substrates, acts on carboxypeptidase Y (cpY/PRC1) to activate it by processing its Pro-peptide. Required for meiosis and spore formation, and for optimal survival in stationary phase. Hydrolysis of proteins with broad specificity, and of Bz-Arg-OEt > Ac-Tyr-OEt. Does not hydrolyze peptide amides. Repressed by glucose. Activated by N- and C-terminal proteolytic cleavage. Protease B (PrB/PRB1) processing requires at least 4 cleavages. First, the signal peptide is removed from the 76 kDa preproprotease B by signal peptidase in the ER. Then, PrB removes its own Pro-region (in trans) at the N-terminus, producing a 39 kDa form before exiting the ER. In the Golgi complex, the C-terminal Post-region of the 40 kDa proprotease B undergoes protease A (PrA/PEP4)-mediated processing to a 37 kDa intermediate, which in turn is quickly processed again by PrB in trans to yield the 31 kDa mature PrB. Glycosylated. Preproprotease B is a 76 kDa unglycosylated precursor that enters the endoplasmic reticulum (ER), where it receives one Asn-linked and an undetermined number of non-Asn-linked carbohydrate side chains. In the Golgi complex, the 39 kDa form becomes 40 kDa, due to elaboration of the Asn-linked side chain. The ultimate processing step removes a peptide containing the Asn-linked chain. Mature PrB has only non-Asn-linked carbohydrates. [beta] is the prion form of PrB. In contrast to other prions, [beta] is not the result of a conformational change of the cellular PrB, but distinguishes itself by autoactivation in trans. Usually, PrB is already involved in its own maturatiuon, but PrA plays a critical role. PrpA mutants lack PrB. However, in growth conditions that favor PRB1 expression, PrB activity persists in PrA mutants due to autocleavage of PrB in trans. This condition is stably transmitted to daughter cells in mitosis. [beta] can be cured by growing in PRB1-repressing conditions. Once a cell has lost PrB activity, it remains stably inactive. Thus, there are 2 alternative states, that are chromosomally identical, but phenotypically distinct. Since PrA is able to activate PrB, normal cells always carry the [beta] prion. Its absence and transmission are only observable in the absence of PrA. Present with 1600 molecules/cell in log phase SD medium. Belongs to the peptidase S8 family.