Chalfie, M., Tu, Y., Euskirchen, G., Ward, W. W., and Prasher, D. C.
Green Fluorescent Protein as a Marker for Gene Expression.  Science 263: 802-804 (1994).

A complementary DNA for the Aequorea victoria green fluorescent protein (GFP) produces a fluorescent product when expressed in prokaryotic (Escheria coli) or eukaryotic (Caenorhabditis elegans) cells. Because exogenous substrates and cofactors are not required for this fluorescence, GFP expression can be used to monitor gene expression and protein localization in living organisms.