FIG. 4.

Med6 and Srb6 associate with Srb4. (A to C) Pairwise interactions of Med6 with Srb proteins. An insect cell extract containing one recombinant protein was incubated with an extract containing equimolar amounts of another recombinant protein which lacked (lanes 1 and 3) or contained (lanes 2 and 4) the FLAG epitope tag. Ovalbumin (Ova) was added to each reaction mixture to serve as a control for specific immunoprecipitation. The epitope-tagged Med6 or Srb4 and bound proteins were immunoprecipitated with anti-FLAG antibody. Fractions (1/10) of the load (IN) and all of the pellets (OUT) were analyzed by Western blotting with specific antibodies. A schematic interpretation of the binary interactions is presented at the top of each panel. (D) Insect cell extracts containing Med6 and Srb proteins were subjected to coimmunoprecipitation with anti-FLAG antibody. In the control reaction (lane 1, no tag), no tagged recombinant was included. In the other reactions, either Med6 (lane 2, tagged Med6) or Srb4 (lane 3, tagged Srb4) contained FLAG epitope tag. (E) A model depicting interactions between Med6 and dominant Srb proteins. This model assumes the stoichiometric association of the five proteins.