The cAMP Receptor Protein (CRP) of Escherichia coli requires a conformational change induced by the binding of cAMP in order to function as a site-specific DNA-binding protein. An intrinsic fluorescence study showed that the tryptophan residues at position 13 and 85 within CRP were located in an internal, nonpolar environment, and the conformational change induced by the binding of cAMP occurred around the tryptophan residue NMR experiment has manifested that the comformational change around the tryptophan residue at position 85 and histidine residue at position 159 of CRP is induced by the binding of cAMP. An extrinsic fluorescence study showed that the distance between the two cysteine 178 residues in the dimer was within about 3.5 A. This distance didn't exhibit a large change upon cAMP binding.