In the eukaryotic nucleus, genetic information is stored within the intimate 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 ~146 bp of DNA wrapped around an octamer of histones containing two copies each of four core histones, H2A, H2B, H3 and H4. We have developed model systems to study the mechanisms by which steroid receptors control many physiological activities by regulating gene expression within this chromatin organization. Our studies have focused on the glucocorticoid receptor (GR) and its ability to remodel chromatin which is mediated by BRG1 ATPase as part of the human SWI/SNF complex. We demonstrate that transactivation from a chromatin template requires an intact BRG1 remodelling activity, and this activity cannot be substituted by other ATP-dependent remodelling proteins. Further, we have designed, characterized and utilized BRG1 truncation and deletion mutants in a series of assays which allow independent evaluation of transcriptional activation and chromatin remodelling by the GR. Our results suggest BRG1 may contain previously uncharacterized functional motifs important for transcriptional activity. Finally, they reveal that protein-protein interactions both within the complex as well as between the remodelling complex and nuclear receptors necessary and sufficient for glucocorticoid receptor functions in vivo.