Gag interactions with host proteins Staufen1 and IMP1 occur in the cytoplasm and at the plasma membrane of transfected HeLa and Jurkat T cells as determined by BiFC. (A) Top - schematic representation of BiFC method. Bottom - Rev-dependent Gag-VN and Gag-VC were co-transfected with pCMV-Rev in HeLa cells. At 24 hr post-transfection, cells were imaged by laser scanning confocal microscopy to detect BiFC. The white arrows indicate plasma membrane concentrated accumulations of Gag-Gag BiFC signals. (B) Gag-VN and Staufen1-VC (top panels) or Gag-VN and IMP1-VC (bottom panels) interactions identified by BiFC. BiFC signals for these interacting pairs were mainly detected in the cytoplasm (indicated by white arrows) and at or near the plasma membrane. (C) Interactions between Gag-VN with IMP1-KH(1-4)-VC (top) and with IMP1-RRM(1-2)-VC (bottom) as determined by BiFC analysis. Evidence for interaction is demonstrated by a green fluorescence signal. (D) The interaction between Gag-VN and Gag-VC (top) or Gag-VN and Staufen1-VC (bottom) was determined by BiFC in Jurkat T cells. Magnified sections demonstrate details on the shapes of BiFC signals/complexes. The size bars are equal to 10 μm.