The β-box is an ERβ-specific NR box. (A) Interactions of VP16-NR fusions with the Gal-β-box fusion or a GAL-GRIP1 (amino acids 610–770) control were determined in HeLa cell transfections. A representative experiment is shown. (B) Peptide competitions for ERα and ERβ binding to GST-GRIP1. Experiments utilized 10μg of competitor (C) Mutation of the β-box to resemble a consensus LXXLL motif. The panel shows the results of a mammalian two-hybrid assay in which binding of Gal-N-CoR or Gal-N-CoR T2402L to VP16-ERβ or VP16-ERα was assayed.