Contributes to endopeptidase activator activity. Acts upstream of or within antigen processing and presentation of exogenous antigen. Predicted to be active in cytoplasm and nucleoplasm. Is expressed in several structures, including heart; hemolymphoid system; liver; lung; and pancreas. Orthologous to human PSME2 (proteasome activator subunit 2). [provided by Alliance of Genome Resources, Apr 2022]