Fluorescence properties of E2-Orange. Shown are (A) excitation and emission and (B) absorbance spectra of E2-Orange. (C) Maturation kinetics of E2-Orange fluorescence. For these measurements the FPs were excited at 520 ± 10 nm excitation and emission was recorded at 560 ± 10 nm. (D) Photobleaching kinetics of E2-Orange (black line), mOrange2 (blue line), KO (gray line), and mKO2 (red line) during widefield fluorescence microscopy. Data were collected using a Texas Red filter set. For (C) and (D), data represent the mean of three independent measurements.