Fig. 5. Epistatic analysis of the light-dependent architectural changes. (A–F) Ultrastructural EM cross-sections of a single rhabdomere. (G–H) Immunogold EM labeling of DGqα as in Figure 2. Scale bar = 500 nm in all panels. (A and B) The near absence of DGqα in the Gαq¹ mutant abolishes the light-dependent morphological changes, showing that DGqα is necessary for the morphological transformation. However, these changes are also blocked in the norpA^P24 mutant (C and D) and in the trp^P343 mutant (E and F), showing that DGqα is not sufficient to bring about these changes. As the trp^P343 mutant also blocks the translocation of DGqα outside the rhabdomere (G and H), it seems that the morphological changes are required to enable DGqα to migrate outside of the rhabdomere. Similar observations were made in four or five different flies.