Proteasome subunit beta type-9(PSMB9) belongs to the proteasome B-type family which is a 20S core beta subunit. PSMB9 is positioned in the class II region of the MHC(major histocompatibility complex). Expression of the PSMB9 protein is induced by gamma interferon and this gene product replaces catalytic subunit 1(proteasome beta 6 subunit) in the immunoproteasome.