A BLUE FLUORESCENT PROTEIN FROM A YELLOW-EMITTING LUMINOUS BACTERIUM

Vibrio fischeri strain Y1 emits yellow light in vivo due to the participation of a yellow fluorescent protein (YFP) in the luciferase reaction. In this study it was found that the organism also produces a protein (referred to as Y1-BFP) emitting strong blue fluorescence. Its molecular weight, about 25 kDa, is the same as or very close to that of YFP. The fluorescence excitation and emission maxima of the purified Y1-BFP are at 416 and 461 nm, respectively, and the fluorescence lifetime is 12.5 ns at 2 degrees C. The molar extinction coefficient of Y1-BFP at 416 nm was estimated to be approx. 9500. With the homologous luciferase, Y1-BFP decreases the intensity and rate of decay in the in vitro reaction but has no effect on its emission spectrum (in contrast to YFP, which has a striking effect on the spectrum). With luciferase isolated from Vibrio harveyi, however, Y1-BFP causes a small blue-shift (approximately 10 nm) in the emission of the enzyme catalyzed reaction, whereas YFP has no effect on the emission spectrum.