Fig. 2. The N-terminus of Srb7p is necessary and sufficient for the interaction with Tup1p. (A) Tup1p interacts with Srb7p in vivo. Serial dilutions of cells expressing the depicted fusions were spotted onto control plates selecting for the presence of these fusions, onto the same plates lacking uracil and onto plates also containing FOA. Interactions are revealed by the lack of growth on the plates without uracil and by growth on the plates containing FOA. (B) Tup1p interacts with Srb7p in vitro. GST-pulldown assays with the depicted proteins purified from E.coli were loaded onto an SDS gel, and HA-Tup1p was detected in a western blot with the help of an α-HA antibody.