Pigment protein. Exhibits a smaller absorbance peak at 525 nm. Has a strong fluorescence emission spectrum which peaks at 611 nm. Monomer. Contains a chromophore consisting of modified amino acid residues. The chromophore is formed by autocatalytic backbone condensation between Xaa-N and Gly-(N+2), oxidation of Tyr-(N+1) to didehydrotyrosine, and formation of a double bond to the alpha-amino nitrogen of residue Xaa-N. Maturation of the chromophore requires nothing other than molecular oxygen. Fluorescent proteins 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. The emission does not change over the pH range of 4 to 10. Maturation occurs via a green intermediate and is complete within 12 hours. Recombinant expression at high temperatures induces oligomerization. Belongs to the GFP family.