2 ACTIVE FORMS OF THE ACCESSORY YELLOW FLUORESCENCE PROTEIN OF THE LUMINOUS BACTERIUM VIBRIO-FISCHERI STRAIN-Y1

In addition to the typical blue luminescence (peak wavelength, approximately 490 nm), the light emission of the luminous bacterium Vibrio fischeri strain Y1 has a yellow component (peak, approximately 540 nm). This is attributable to an accessory ''yellow fluorescence protein'' (YFP; M(r) almost-equal-to 25 kDa), which acts in conjunction with the enzyme luciferase and possesses a flavin chromophore. Cell extracts contain two such YFPs in approximately equal amounts. Both have activity in vitro and are otherwise similar in the several respects examined. The possibility that they represent subunits of a heterodimer was examined, but no dimeric protein could be demonstrated.