Based on a mouse study, the outer ring of the spermatoproteasome 20S core particle (20S sCP), whose alpha-4 (PSMA7) subunit is replaced with the spermatoproteasome-specific subunit alpha-4s (PSMA8), interacts with the inner beta ring composed of canonical beta subunits (Uechi et al. 2014). As the role of the PSMG1:PSMG2 complex in the context of spermatoproteasome has not been examined and as spermatoproteasomes were shown to interact with significantly less POMP than canonical proteasomes (Zivkovic et al. 2022: bovine model system), these three proteins are not shown as components of half-spermatoproteasomes.