Anti-PSME4 antibodies are used in the immunodetection of the protein proteasome activator subunit 4. In humans, the canonical protein has a reported length of 1843 amino acid residues and a mass of 211.3 kDa. Its subcellular localization is in the nucleus and cytoplasm. Up to 4 different isoforms have been reported for this protein. It is notably widely expressed in many tissue types. A member of the BLM10 protein family, PSME4 is reported to be an associated component of the proteasome that specifically recognizes acetylated histones and promotes ATP- and ubiquitin-independent degradation of core histones during spermatogenesis and DNA damage response. Synonyms for this target antigen include proteasome activator complex subunit 4, proteasome (prosome, macropain) activator subunit 4, proteasome activator 200 kDa, proteasome activator PA200, and PA200. PSME4 gene orthologs have been reported in the mouse, rat, bovine, frog, chimpanzee and chicken species.