Fig. 10. Putative model of the light-dependent translocation cycle of DGqα in Drosophila photoreceptors. The numbers represent discreet steps in the translocation cycle of DGqα. (1) Light-activated rhodopsin activates DGq by catalyzing the exchange of GDP for GTP. This causes the GTP-bound α-subunit to dissociate from the βγ subunits. The dissociated βγ subunits are not shown. (2) The activated α-subunit proceeds to activate its effector, PLC. The latter, in turn, accelerates the turn off (GTPase) of the DGqα protein. (3) Alternatively, the activated α-subunit is subject to depalmitoylation and translocates to the cytosol. (4) The inactivated DGqα returns to the membrane in a βγ-dependent process, followed by palmitoylation and attachment to the membrane (according to the ‘two-signal model’).