CLIP is a regulatory domain which controls the proteinase action of various proteins of the trypsin family, e.g. easter and pap2. The CLIP domain remains linked to the protease domain after cleavage of a conserved residue which retains the protein in zymogen form. It is named CLIP because it can be drawn in the shape of a paper clip. It has many disulphide bonds and highly conserved cysteine residues, and so it folds extensively.