ABSTRACT:
      The green fluorescent protein(GFP) from the Pacific Northwest Aequorea Vicoria  has generated intense intest as a marker for gene exression and localization of gene products.  The chromophore, resulting fomr the spontaneous cyclization and oxidation of the sequence -Ser65(or Thr65)-Tyr66-Gly67-, requires the native protien fold for both formation and fluorescence emission.  The structure of Thr65 GFP has been determined at 1.9A resolution.  The protein fold consists of an 11-stranded beta barrel with a coaxial helix, with the chromophore forming from the central helix.  Directed mutagenesis of one residue adjacent to the chromophore, Thr203, Tyr or His results in significantly red-shifted excitation and emission maxima.