Now, what exactly are the function of these 219s subunits? Well, it's the 19s subunits that essentially locates and binds to the polyubiquid native protein and once it locates it it has Atpa's activity that allows the 19s regulatory subunits to actually begin unfolding that protein. Why do we need to unfold the protein? Well, because we need to fit the protein into the 20s core. And so it's the 19s regulatory subunit that binds to the polyubiquitinated protein. It begins using ATP molecules to basically unfold that protein and insert that protein into the 20s core.