Non-fluorescent pigment protein that is lilac in color. Fluorescence excitation of HcRed mutant is at 592 nm and emission at 645 nm. Homotetramer. 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. The precise stereochemistry of the tyrosine has not been determined. 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. In the wild-type form, the chromophore matures at 20 degrees Celsius. Mutants have been selected to mature at 37 degrees Celsius to make them suitable for use in vivo and cell culture. Belongs to the GFP family.