Energy-transfer acceptor. Its role is to transduce the blue chemiluminescence of the protein aequorin into green fluorescent light by energy transfer. Fluoresces in vivo upon receiving energy from the Ca(2+)-activated photoprotein aequorin. Exhibits a smaller absorbance peak at 470 nm. The fluorescence emission spectrum peaks at 507-510 nm with a shoulder at 545 nm (PubMed:8137953, PubMed:9154981). The exact value of the emission maximum depends on the environment of the chromophore (PubMed:10220315). As a consequence, mutant versions have been designed that have substantially shifted emission spectra, including yellow-emission variants (YFP), blue and cerulean fluorescing proteins (PubMed:9145105, PubMed:9782051, PubMed:17685554). Monomer. Photocytes. Contains a chromophore consisting of modified amino acid residues. The chromophore is formed by autocatalytic backbone condensation between Ser-65 and Gly-67, and oxidation of Tyr-66 to didehydrotyrosine. Maturation of the chromophore requires nothing other than molecular oxygen. Green fluorescent protein has been engineered to produce a vast number of variously colored mutants, fusion proteins, and biosensors. Green fluorescent protein can be mutated to emit at different wavelengths such as blue for BFP (when Tyr-66 is replaced by His), cyan for CFP (when Tyr-66 is replaced by Trp), and yellow for YFP (when THR-203 is replaced by Tyr). Further generation of mutants led to more stable proteins (at 37 degrees Celsius for example) with brighter fluorescence and longer fluorescence lifetimes. Fluorescent proteins and their mutated allelic forms have become a useful and ubiquitous tool for making chimeric proteins, where they function as a fluorescent protein tag. Typically they tolerate N- and C-terminal fusion to a broad variety of proteins. They have been expressed in most known cell types and are used as a noninvasive fluorescent marker in living cells and organisms. They enable a wide range of applications where they have functioned as a cell lineage tracer, reporter of gene expression, or as a measure of protein-protein interactions (PubMed:17685514, PubMed:17685554, PubMed:8578587, PubMed:8707053, PubMed:9145105, PubMed:9154981, PubMed:9759496, PubMed:9782051). Can also be used as a molecular thermometer, allowing accurate temperature measurements in fluids. The measurement process relies on the detection of the blinking of GFP using fluorescence correlation spectroscopy (PubMed:17685514). Belongs to the GFP family. The greenest of us all - Issue 11 of June 2001 Paint my thoughts - Issue 108 of August 2009 Green fluorescent protein entry