Enables lysine-acetylated histone binding activity and peptidase activator activity. Involved in DNA repair; proteasomal ubiquitin-independent protein catabolic process; and spermatogenesis, exchange of chromosomal proteins. Located in cytosol and nucleus. Part of spermatoproteasome complex. Is expressed in craniocervical region bone; ganglia; sensory organ; and submandibular gland primordium. Used to study visceral heterotaxy. Orthologous to human PSME4 (proteasome activator subunit 4). [provided by Alliance of Genome Resources, Apr 2022]