The article reports on a protein tag that simplifies labeling and visualization of synthesized target proteins in tissue and whole animals. Michael Lin and colleagues at Roger Tsien's laboratory at the University of California have developed the idea of a self-cleaving tag containing a protease that could be inhibited by a drug. The team designed a cassette called TimeSTAMP that encodes the NS3 protease from hepatitis C virus flanked by two cleavage sites.