Proteasome Activator Subunit 4 (PSME4)

PA200 purified from bovine testis activated proteasomal hydrolysis of peptides, but not proteins.The deduced 1,843-amino acid proteins share over 90% sequence identity. PA200 contains a bipartite nuclear targeting sequence and several potential phosphorylation sites, many of which are sites for the DNA repair kinases ATM and PRKDC. Two-dimensional gel electrophoresis of bovine testis PA200 resolved the 200-kD band into several isoelectric variants that were unaffected by phosphatase treatment. Western blot analysis of mouse tissues detected 3 species: a 200-kD species that was most abundant in testis; a 60-kD species that was most prominent in brain but also abundant in liver and lung; and a 160-kD species that was abundant in other organs.