Identification of the N-terminal region of Stau155 as a regulatory sequence for HIV-1 assembly. (A, B) 293T cells were transfected as described in Figure 4B but included additional Stau155-HA deletion mutants. (A) For each condition, an aliquot of the cells (providing equivalent total YFP/Rluc ratio) was used for Western blot analysis using anti (α)-HA and anti (α)-CA antibodies. Anti (α)-GAPDH antibody was used as a loading control. (B) Another aliquot of the cells was used for BRET assays. Calculated BRET ratios were plotted as a function of the corresponding total YFP/Rluc ratio. (C, D) Dose response pr55Gag/pr55Gag BRET assays. 293T cells were transfected with fixed amounts of pCMV-pr55Gag-Rluc and pCMV-pr55Gag-YFP and increasing amounts of different Stau1-HA expressors. (C) 48 hours later, half of the cells were lysed and analyzed by Western blotting using anti (α)-HA and anti (α)-GAPDH antibodies. *: Non-specific labelling.(D) The other half of the cells was used for BRET assays. BRET ratio is plotted as a function of the corresponding amount of transfected Stau1-HA expressor.