DNA-BINDING SPECIFICITY AND FUNCTION OF RETINOID-X RECEPTOR-ALPHA

Retinoid X receptors are members of the erbA superfamily of ligand-ind ucible transcription factors. Similar to several other members of this gene family, retinoid X receptors are known to bind to the hexameric DNA sequence AGGTCA. After binding to a direct repeat of this hexamer with a one base pair spacer, retinoid X receptor homodimers are able t o activate transcription in the presence of the ligand 8-cis-retinoic acid. However, it is not known if AGGTCA represents the highest affini ty binding site for retinoid X receptors. A combination of the electro phoretic mobility shift assay and polymerase chain reaction was used t o isolate from a pool of random DNA those sequences that bind retinoid X receptors with highest affinity. This approach, combined with mutat ional analysis and DNA footprinting, led to the identification of the seven-base pair sequence GGGGTCA as the highest affinity retinoid X re ceptor binding site. A direct repeat of this sequence is substantially more active than a direct repeat of AGGTCA as a retinoid X response e lement.