Fig. 4. G_q translocation requires the light-activation of rhodopsin, but does not require the activation of the phototransduction components downstream of G_q. (A) Cross-sections of the wild type (WT) and null mutants in Rh1 (ninaE^I17), PLC (norpA^P41), TRP (trp³⁴³) and PKC (inaC¹⁰⁹), all stained with anti-G_q antibody. All flies were either dark raised or light exposed for 2 hours (3000 lumens meter^-2). In ninaE^I17, G_q is rhabdomeric in both dark and light conditions. A low level of G_q signal was seen in cell bodies, consistent with previous reports showing that ninaE mutants display subrhabdomeric invaginations into the cell bodies (Leonard et al., 1992; O'Tousa et al., 1989). The remaining null mutants displayed rhabdomeric localization of G_q in the dark and translocation of G_q upon illumination. This suggests that rhodopsin is necessary for translocation of G_q, whereas PLC, TRP and PKC are not. (B) G_q undergoes a light-dependent shift to membranes in trp³⁴³ null mutants similar to WT. Dark-adapted WT and trp³⁴³ flies were exposed to white light (50.7x10³ lumens meter^-2) for 2.5 hours. Membrane and corresponding cytosolic fractions were isolated for immunoblot analysis. The bar graph shows the proportions of total G_q present in the membrane and cytosolic fractions for dark-adapted and light-exposed flies. DC, dark-adapted cytosolic fraction; DM, dark-adapted membrane fraction; LC, light-exposed cytosolic fraction; LM, light-exposed membrane fraction. The trp³⁴³ null mutants displayed a light-dependent shift of G_q from the membrane-associated fraction to the cytosolic fraction that was not significantly different from the wild type. WT: DM, 81.5±6.0%; LM, 13.2±9.6%; trp: DM=81.5±10.5%, LM=4.2±1/3%. A representative immunoblot is shown above the graph. SEMs are indicated