Figure 4.

SOS2 interacts with SOS3 in vitro. (A) Interaction between SOS3 and SOS2 in a pull-down assay. [³H]leucine-labeled SOS3 was incubated with glutathione-Sepharose immobilized GST, GST fusion proteins of SOS2, or RB. Proteins bound to the Sepharose beads were pelleted, washed thoroughly, electrophoresed, and detected by fluorography. (B) Interaction between SOS3 and SOS2 in a gel blot overlay assay. GST, partially purified GST-RB, GST-SOS2, GST-SOS2(K40N), GST-SOS2(G197E), and protein size markers (M) were separated by SDS/PAGE. Two identical gels were run; one was stained with Coomassie blue (Left), and the other was electroblotted and probed with [³²P]labeled SOS3 (Right).