Normalized spectra for selected mutants of asCP and DsRed. Absorption (black solid lines), excitation (colored dashed lines), and emission (colored solid lines) spectra are shown for each mutant. Blue, green, or red excitation-emission lines correspond to color of fluorescence. (A) asCP-S165V. Blue fluorescence is about tenfold weaker than red. (B) asCP-S165A. (C) asCP-S165C. (D) asCP-S165T. Green emision is about twofold stronger than red. (E) DsRed-NF. Green emission peak is about threefold lower than red one.