Figure 3.

Energy-level diagrams of the red-shifted mutants RS-GFP (Top), S65T (Middle), and EYFP (Bottom). The forms A, I, and B photointerconvert as indicated by the diagonal arrows. The relative populations of the three forms differ for the various mutants. In RS-GFP only the I-form is populated at 1.6 K before burning; by burning into I, the A- and B-forms are photoinduced. In S65T, all forms are populated at 1.6 K, with the I-form having the lowest ground-state level. In EYFP, the most populated form is B; I and A are significantly less populated at 1.6 K. Their populations can be enhanced by burning into B.