Interaction between SOS3 and SOS2, SOS2 N-terminal (SOS2-NT) and C-terminal (SOS2-CT) domains, and SIP1, SIP2, SIP3, or SIP4 in the yeast two-hybrid assay. Yeast strains containing pAS-SOS3 and pACT-SOS2, pACT-SOS2-NT, pACT-SOS2-CT, pACT-SIP1-1, pACT-SIP2-1, pACT-SIP3-1, pACT-SIP4-1, respectively, were assayed for LacZ expression. pAS-p53 and pAS2 were used as negative controls in combination with pACT-SOS2. (Upper Right) Yeast grown on SC medium minus tryptophan and leucine to select for both the bait and prey proteins. (Lower Right) SC medium minus tryptophan, leucine, histidine, and plus 25 mM 3-amino-1,2,4-triazole (AT) to allow the growth of only positively interacting clones.