Mediates receptor recognition and membrane fusion for viral entry.S1 subunit: contains receptor-binding domain (RBD)** which binds to the peptidase domain (PD) of ACE2S2 subunit: responsible for membrane fusion; cleaved by host proteases once S1 binds to ACE2 which is needed for a viral infection to occur. This evidence concerns the gene PSMD1 and viral infectious disease.