The reagent (NucViewTM) consists of a nucleic acid-binding dye with a fluorescent probe that is attached to a four-amino acid peptide sequence DEVD (Asp-Glu-Val-Asp) forming a cell membrane-permeable DEVD-DNA complex. While the nucleic-acid dye is linked to the DEVD peptide sequence, the dye is unable to bind to DNA and remains non-fluorescent. During apoptosis, caspase 3/7 proteins cleave the DEVD-DNA dye complex and thereby release the high-affinity DNA dye, which translocates to the nucleus and binds to the DNA, producing a bright green fluorescent signal.