The present invention provides methods and materials that can be used to detect, examine and exploit protease mediated protein expression. An illustrative embodiment of the invention is a polynucleotide encoding a polypeptide having a plurality of operatively linked elements comprising a polypeptide degradation signal that functions as a proteosome substrate; a polypeptide of interest having an observable activity; and a linker disposed between the polypeptide degradation signal and the polypeptide of interest. The linker comprises a protease recognition motif that is capable of being specifically recognized and cleaved by a protease. The activity of the polypeptide of interest is observed when the motif is specifically recognized and cleaved by the protease; and the activity of the polypeptide of interest is decreased or not observed when the motif is not specifically recognized and cleaved by the protease.