green fluorescent protein (gfp) is also a photoprotein isolated and cloned from the jellyfish "aequorea victoria". variants have also been isolated from the sea pansy "renilla reniformis". gfp, like aequorin, produces a blue fluorescent signal, but without the required addition of an exogenous substrate. all that is required is an ultraviolet light source to activate the fluorescent properties of the photoprotein. this ability to autofluoresce makes gfp highly desirable in biosensing assays since it can be used on-line and in to monitor intact, living cells. additionally, the ability to alter gfp to produce light emissions besides blue (i.e., cyan, red, and yellow) allows it to be used as a multianalyte detector. consequently, gfp has been used extensively in bioreporter constructs within bacterial, yeast, nematode, plant, and mammalian hosts.