Abstract: Green fluorescent protein (GFP) is produced by the bioluminescent jellyfish Aequorea victoria.GFP fluoresces in the lower green portion of the visible spectrum and has been found useful in biological research.GFP does not require a specific cellular environment to become fluorescent and can be artificially expressed in cell types as diverse as bacterial, plant, and animal cells.GFP can be attached to other proteins of interest using recombinant DNA techniques. Thus, it is possible to trace the synthesis, location, and movement of these proteins in single living cells using conventional fluorescence microscopy.Improved variants of GFP have been devised that are brighter than the original and show a preference for blue light (which is nontoxic to cells) rather than ultraviolet light (which can rapidly kill cells being observed)