Gaussia Luciferase (GLuc) is a 20 kDa luciferase from the marine cocepod Gaussia princeps. This luciferase, which does not require ATP, catalyzes the oxidation of the substrate coelenterazine in a reaction that produces light (480 nm), and has considerable advantages over other luminescent reporter genes. It is normally secreted from the cells and its secretion signal also functions very efficiently in mammalian cells. GLuc offers the advantage of a greatly increased bioluminescent signal relative to the commonly used firefly (Fluc) and Renilla luciferases (RLuc). GLuc was determined to emit light with a specific activity of 4.2 x 1024 photons/s/mol, the highest reported activity for any characterized luciferase (1).