FIGURE 4.

BRET experiments in HEK-293 cells. BRET was measured in HEK-293T cells co-expressing D₃-Rluc and D₁-YFP (closed squares) or D₃-Rluc and CXCR4-YFP (open squares) constructs. Co-transfections were performed with increasing amounts of plasmid DNA for the YFP construct (1 μg of DNA to 10 μg of DNA), whereas the DNA for the Rluc construct was maintained constant (3 μg). Both fluorescence and luminescence of each sample were measured prior to every experiment to confirm equal expression of Rluc while monitoring the increase of YFP expression. The relative amounts of BRET acceptor are expressed as the ratio between the fluorescence of the acceptor and the luciferase activity of the donor. “YFP₀” corresponds to the fluorescence value in cells expressing the BRET donor alone. BRET data are expressed as means ± S.D. of three to nine different experiments grouped as a function of the amount of BRET acceptor.