Cellular component

A proteasome specifically found in mammalian testis. Contains the proteasome activator PA200 in the regulatory particle, and beta1i, beta2i, beta5i and/or alpha4s in the core (20S) subunit. Beta1i, beta2i and beta5i are inducible catalytic subunits, closely related to beta1, beta2 and beta5. Alpha4s is a sperm-specific 20S subunit, but unlike other alternative 20S subunits alpha4s lies in the outer alpha-ring and lacks catalytic activity.