FIG. 1.

Clone S1 encodes a protein that specifically interacts with Smad1 in yeast two-hybrid assays. (A) The clone S1 was repeatedly isolated from a two-hybrid screen for gene products that interact with Smad1 but not with Smad2. In the forward two-hybrid assay, S1 was cotransformed with different bait constructs (GAL4DB domain fused with Smad1, Smad2, Lamintin, or the empty bait vector) into AH109 yeast cells. The growth of transformants on selective medium (lacking Trp, Leu, Ade, and His) indicates interaction between prey and bait. (B) In a reciprocal two-hybrid assay, the insert of S1 was fused with the GAL4DB domain in the bait vector, which was then cotransformed with the prey vector or prey vector containing Smad1, Smad2, or an unrelated gene (large T antigen) into AH109 yeast cells. Transformants were plated on selective medium (lacking Trp, Leu, Ade, and His). In both A and B, two independent colonies are shown for each interaction examined. DB, GAL4 DNA binding domain. AD, GAL4 activation domain.