PSMB9, also known as proteasome subunit beta type-9, is a member of the proteasome B-type family, also known as the T1B family, that is a 20S core beta subunit. This protein is located in the class II region of the MHC (major histocompatibility complex). Expression of this protein is induced by gamma interferon and this gene product replaces catalytic subunit 1 (proteasome beta 6 subunit) in the immunoproteasome.