Activation of the mouse mammary tumor virus (MMTV) promoter by the glucocorticoid receptor (GR) is18:3633-3644). We have reconstituted MMTV LTR DNA into a polynucleosome array using Drosophila embryo extracts. We show binding of purified GR to specific GR elements within a large, multinucleosome array and describe a GR-induced nucleoprotein transition that is dependent on ATP and a HeLa nuclear extract. Previously uncharacterized GR binding sites in the upstream C nucleosome region are involved in the extended region of chromatin remodeling. We also show that GR-dependent chromatin remodeling is a multistep process; in the absence of ATP, GR binds to multiple sites on the chromatin array and prevents restriction enzyme access to recognition sites. Upon addition of ATP, GR induces remodeling and a large increase in access to enzymes sites within the transition region. These findings suggest a dynamic model in which GR first binds to chromatin after ligand activation, recruits a remodeling activity, and is then lost from the template. This model is consistent with the recent description of a "hit-and-run" mechanism for GR action in living cells

Activation of the mouse mammary tumor virus (MMTV) promoter by the glucocorticoid receptor (GR) is associated with a chromatin structural transition in the B nucleosome region of the viral long terminal repeat (LTR). Recent evidence indicates that this transition extends upstream of the B nucleosome, encompassing a region larger than a single nucleosome (G. Fragoso, W. D. Pennie, S. John, and G. L. Hager, Mol. Cell. Biol. 18:3633-3644). We have reconstituted MMTV LTR DNA into a polynucleosome array using Drosophila embryo extracts. We show binding of purified GR to specific GR elements within a large, multinucleosome array and describe a GR-induced nucleoprotein transition that is dependent on ATP and a HeLa nuclear extract. Previously uncharacterized GR binding sites in the upstream C nucleosome region are involved in the extended region of chromatin remodeling. We also show that GR-dependent chromatin remodeling is a multistep process; in the absence of ATP, GR binds to multiple sites on the chromatin array and prevents restriction enzyme access to recognition sites. Upon addition of ATP, GR induces remodeling and a large increase in access to enzymes sites within the transition region. These findings suggest a dynamic model in which GR first binds to chromatin after ligand activation, recruits a remodeling activity, and is then lost from the template. This model is consistent with the recent description of a "hit-and-run" mechanism for GR action in living cells

In the search for androgen receptor (AR) coregulators, we have recently identified four novel proteins that recognize AR zinc finger region both in vivo and in vitro and activate AR-dependent transcription. One of the proteins is a small nuclear RING finger protein (SNURF) that possesses two interaction interfaces; one for AR and another one for other activators of transcription such as Spl. The second protein is a nuclear Ser/Thr protein kinase (ANPK). This nuclear protein kinase augments specifically AR-dependent transcription, probably through stabilization of receptorcoactivator interactions. The receptor itself does not appear to be a substrate for ANPK. The third protein is dubbed ARIP3-for androgen receptor-interacting protein 3-, and it is a novel member of the so-called PIAS (protein inhibitors for activated STATs) protein family. And finally, the forth protein, termed ARIP4, is a nuclear ATPasc that belongs to the SNFZ-like family. However, it exhibits sequence homology to other