THOMAS SCHLENKRICH, DONAT-P. HÄDER^* and MICHAEL LEBERT

Dictyostelium discoideum amoebae show positive phototaxis at low irradiances (< 0.1 W m-2) and negative phototaxis at higher intensities. Based on the action spectrum for photoaccumulation of amoebae we were able to identify a membrane-bound 45 kDa protein which we assume to be the photoreceptor and/or the antenna pigment for amoebal phototaxis. For further characterization polyclonal antibodies directed against the 45 kDa protein were generated. The amount of protein did not change with the growth conditions (light or dark grown amoebae), but the binding characteristics of the antibody to it’s antigen strongly depended on the availability of light. This finding indicates a light-induced, reversible modification of the putative photoreceptor. The nature of this modification is unknown.