The TimeSTAMPa cassette is a module consisting of the HCV (Hepatitis C virus) NS3 protease, lacking the helicase domain and carrying the slow-cleaving Ala-54 (a) variant, and flanked on both sides by a NS4A/B cleavage site. In the absence of a protease inhibitor, the NS3 protease cleaves at the NS4A/B target site, removing the cassette and any downstream protein sequence from a tagged protein of interest. This cleavage can be inhibited by the addition of the cell-permeable BILN-2061 inhibitor (FBrf0216000).