Proteasome Cleavage Prediction Server (PCPS). A) PCPS interface. B) PCPS result page. The page returns the predicted cleavage score after each residue of the protein query. The residues with a cleavage score above the threshold (0.5) are marked with a tick. These residues correspond to the P1 residue of the cleavage site and determine the C-terminus of MHCI-restricted peptides.