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.