Thyroid hormone receptor dimerization function maps to a conserved subregion of the ligand binding domain

Thyroid hormone receptors (TRs) bind as dimers to specific DNA response elements. We have used a genetic approach to identify amino acid sequences required for dimerization of the TRβ isoform. Bacteria expressing a chimeric repressor composed of the DNA binding domain of the bacteriophage λ cl repressor fused to the TRβ ligand binding domain are immune to λ infection as a consequence of homodimerization activity provided by the receptor sequences. The phenotypes of deletions and point mutations of the TRβ sequences map dimerization activity to a subregion of the ligand binding domain that is highly conserved among all members of the nuclear hormone receptor superfamily. These results confirm and extend previous findings indicating that this subregion plays an important role in the dimerization of TRβ and other superfamily members.