Three segments in the Gal11 N-terminal region function additively to promote binding to Gcn4 in vitro and recruitment to ARG1 in vivo of the Mediator tail in sin4Δ cells, and B-box mutation WQV mimics the Gcn− phenotype of Δ5 in SIN4 cells. A and B, WCEs from transformants of sin4Δ strain IJY6 harboring the indicated myc-GAL11 alleles were incubated with equal amounts of GST, GST-Gcn4 (WT), and mutant GST-Gcn4-Ala10 (10Ala) proteins immobilized on glutathione-Sepharose resin. Bound fractions and 10% of the input yeast WCEs were subjected to Western analysis with antibodies against Snf6 or Spt3, Myc antibodies to detect Myc-Gal11, and HA antibodies to detect HA-Med2. C and D, ChIP analysis of Myc-Gal11 occupancy of the ARG1 UAS in transformants of sin4Δ strain IJY6 harboring the indicated myc-GAL11 alleles, conducted as described in the legend for . At least three independent cultures and two PCR amplifications for each immunoprecipitation were performed for each strain to yield the means ± S.E. (error bars) (n = 6–16) plotted here. E, coimmunoprecipitation analysis of the Mediator tail subdomain in transformants of gal11Δ sin4Δ MED2-HA strain IJY6 containing the indicated myc-GAL11 alleles. WCEs were immunoprecipitated with HA antibodies, and immune complexes were subjected to Western analysis with c-Myc antibodies to detect Myc-Gal11, HA antibodies to detect HA-Med2, or Rpb3 antibodies. I, 5% of input WCE; P, total immunoprecipitate; S, 10% of supernatant. F, complementation of the 3ATS/Gcn− phenotype of gal11Δ by the indicated myc-GAL11 alleles in transformants of strain IJY3, as described in the legend for . G, ChIP analysis of Myc-Gal11 occupancy of the ARG1 UAS in transformants of SIN4 strain IJY3 harboring the indicated myc-GAL11 alleles, as described in the legend for . At least three independent cultures and two PCR amplifications for each immunoprecipitation were performed for each strain to yield the means ± S.E. (error bars) (n = 6–16) plotted here.