The green fluorescent protein (GFP) from the jellyfish Aequorea victoria and its spectral variants yellow (YFP); cyan (CFP) and blue (BFP); as well as the homologous red fluorescent protein from the sea anemone Discosoma sp. (dsRFP) are spontaneously fluorescent proteins. The wild-type green fluorescent protein is a specialised protein that emits fluorescence at 508 nm when exposed to excitation light of 395 nm or 475 nm (see also ‘Aequorin’ and ‘Fluorescent and Bioluminescent Proteins’).
Shortly after the initial molecular cloning of the GFP cDNA by Prasher et al. in 1992 it was demonstrated by Chalfie et al. that GFP can be expressed as a functional transgene. When a GFP (or a variant) gene is introduced into a host cell line, the entire cellular cytoplasm will emit fluorescence which can easily be detected with a fluorescence microscope.
GFP related proteins rapidly became important investigational tools in various disciplines associated with life sciences including medicine and biology. They can act as reporter genes for promoter studies or as cell lineage tracers. Another big advantage of GFP for current research lies in its ability to act as an N- or C-terminal protein tag. GFP as well as the fusion partner usually retain their function and depending on the nature of the fusion partner GFP can be directed specifically to different intracellular compartments.