Nuclear hormone receptors activate direct, inverted, and everted repeats

Nuclear hormone receptors comprise a family of ligand-modulated transcription factors that link cellular responses to extracellular and intracellular signals. Receptors for retinoids, thyroid hormone, vitamin D3 and fatty acids/peroxisome proliferators bind their response elements as heterodimers with the retinoid X receptor. Naturally occurring response elements are composed of core-motifs that are organized as direct, inverted, and/or everted repeats. The structural mechanisms that facilitate binding of a single receptor heterodimer to such diverse binding sites remain unknown.