FIG. 7.

The RNA-binding domain of a single interacting partner of the Caprin-1-G3BP-1 complex is necessary and sufficient for the entry of the complex to SG. (A) HeLa cells were cotransfected with plasmids encoding Flag-G3BP-1 and those expressing GFP fusions of fragments of Caprin-1, namely GFP-Caprin-1 (1 to 606), GFP-Caprin-1 (352 to 606), or GFP-Caprin-1 (1 to 327). After 48 h, the cells were stained for Flag (red). Nuclei were stained with DAPI. None of these Caprin-1 fragments induce SG formation when expressed alone (data not shown). However, when coexpressed with Flag-G3BP-1, the Caprin-1 fragments 1 to 606 and 352 to 606 colocalized with G3BP-1-induced SG, but the Caprin-1 fragment, 1 to 327, that lacks the motif for binding G3BP-1 did not. (B) 293T cells were transfected with plasmid expressing GFP fused to a 29-amino-acid peptide from Caprin-1, GFP-Caprin-1 (352 to 380) with or without Flag-G3BP-1. After 48 h, the cells were fixed and stained for Flag (red). Nuclei were stained with DAPI. Note that the GFP-Caprin-1 (352 to 380) entered SG formed in cells coexpressing G3BP-1. (C) The NTF-2-like domain of G3BP-1 enters SG only when coexpressed with Caprin-1. HeLa cells were transfected with the GFP fusion of the fragment of G3BP-1 corresponding to the NTF-2 like domain, GFP-G3BP-1 (1 to 141), with and without Flag-Caprin-1. After 48 h, the cells were fixed and stained for Flag (red). Nuclei were stained with DAPI. Note that in cells overexpressing Flag-Caprin-1, the GFP-G3BP-1 (1 to 141) relocated from the nucleus into the cytoplasmic SG that were induced by overexpression of Flag-Caprin-1.