UASt regulatory sequences drive expression of 'SR4VH', a fluorescent sensor for effector caspase activity. The sensor is a fusion protein composed of the Tag:Myr(Src64B) membrane localization signal, mRFP1, four tandem repeats of the amino acid sequence DEVD, Venus and a strong nuclear localization signal (Tag:NLS(His2B)). In the the absence of effector caspase activation the entire fusion protein is tethered to the cellular membranes outside the nucleus (due to the presence of the Tag:Myr(Src64B) tag). In the presence of an active effector caspase, the protein can be cleaved at the DEVD linker, releasing the Venus-Tag:NLS(His2B) moiety and allowing its translocation to the nucleus, while the Tag:Myr(Src64B)-mRFP1 moiety remains tethered at the membrane.