Viral RNA-binding proteins, TGBp1 and CP, interact with TGBp2 in the ER. (A, top left) The scheme of a BiFC assay. Vn tag was fused to a protein of interest termed A, and Vc tag was fused to protein B. The formation of a complex between A and B brings Vn and Vc in close enough proximity to fold into a fluorescent YFP (Venus). (A, top right) Positive interactions among BaMV proteins by BiFC. (A, bottom left) Images of center or periphery of yeast cells (CWY4128) expressing Sec61-CFP and BiFC constructs indicated by fluorescence microscopy. White arrowheads denote the BiFC-positive signals on ER sheets. (A, bottom right) Peripheral views of yeast cells (CWY4093) expressing the Rtn1-mCherry, CFP-TGBp3, and BiFC constructs indicated were imaged by fluorescence microscopy. White arrowheads denote the BiFC-positive signals on ER tubules. Bars, 5 µm. (B, left) Peripheral views of N. benthamiana cells expressing the CFP-AtSec61γ and BiFC constructs indicated were imaged by confocal microscopy. White arrowheads denote the BiFC-positive signals on ER sheets. (B, right) Peripheral views of N. benthamiana cells expressing the mCherry-TGBp3, CFP-AtSec61γ, and BiFC constructs indicated were imaged by confocal microscopy. White arrowheads denote the BiFC-positive signals on ER tubules. Bars, 10 µm. (C) A model for the potexviral RNP complex. TGBp3 forms a stoichiometric complex with TGBp2, which interacts with two RNA-binding proteins (TGBp1 and CP) in the ER. The sorting signal in TGBp3 directs the targeting of the RNP to highly curved ER structures near plasmodesmata for viral cell-to-cell movement. Whether the viral RNA is delivered to the neighboring cells with RNP or only with TGBp1 is unclear.