Description_x000D_ Biochem/physiol Actions_x000D_ Nuclear receptors form the largest known family of transcription factors and have a crucial role in nearly all aspects of vertebrate development and adult physiology by transducing the effects of hormones into transcriptional responses. The family is defined by two domains: (α) the central, highly conserved, DNA-binding domain (DBD) of approximately 66 amino acids, and (β) the C-terminal, structurally conserved, ligand-binding domain (LBD) of approximately 250 amino acids. The amino-terminal regions are least conserved among nuclear receptor sequences. This domain is highly divergent between TRα and TRβ isoforms, which suggests differential roles in transcriptional regulation. In addition, alternative splicing of the TRβ gene generates two isoforms, TRβ1 and TRβ2 with completely different amino-terminal domains. Unliganded TR inhibits the formation of a functional pre-initiation complex, through direct interaction with TBP and transcription factor IIB. In addition, in the absence of ligand TR has been shown to repress transcription through recruitment of a corepressor complex, which also includes Sin3A and histone deacetylase. Ligand binding releases the corepressor complex and recruits a coactivator complex that includes multiple histone acetyltransferases, including a steroid receptor family coactivator, p300/CREB-binding protein–associated factor (PCAF), and CREB binding protein (CBP)._x000D_ Physical form_x000D_ Clear and colorless frozen liquid solution_x000D_ Preparation Note_x000D_ Use a manual defrost freezer and avoid repeated freeze-thaw cycles. While working, please keep sample on ice.