Nuclear receptors and chromatin remodeling machinery.

Eukaryotic genetic information is stored within the association of DNA and histone proteins resulting in a dynamic polymer called chromatin. The fundamental structural unit of chromatin is the nucleosome which consists of approximately 146 bp of DNA wrapped around an octamer of histones containing two copies each of four core histones, H2A, H2B, H3 and H4. It is this DNA/protein fiber that transcription factors and other agents of chromatin metabolism must access and regulate. We have developed model systems to study the mechanisms by which steroid receptors control physiological activities by regulating gene expression within a higher order chromatin organization. Our studies have focused on the glucocorticoid receptor and its ability to remodel chromatin which is mediated by the BRG1 complex. Using novel cell systems, we demonstrate that GR-mediated transactivation from chromatin templates requires BRG1 remodeling activity and that other ATP-dependent remodeling proteins cannot substitute for this activity.