Binding of the glucocorticoid receptor induces a topological change in plasmids containing the hormone-responsive element of mouse mammary tumor virus.

Glucocorticoid hormones stimulate transcription of the mouse mammary tumor virus (MMTV) promoter by means of an interaction of the hormone receptor with a set of upstream DNA-binding sites called the hormone-responsive element (HRE). In an attempt to understand the underlying molecular mechanism, we have analyzed the influence of receptor binding on the topological state of plasmids carrying different parts of the HRE. Incubation of negatively supercoiled plasmids containing the intact HRE with the 94-kD purified glucocorticoid receptor, followed by extensive digestion with topoisomerase I, leads to a distribution of topoisomers shifted by two turns toward positively supercoiled circles. If relaxed plasmids are incubated with receptor and treated with topoisomerase I, the average linking number of the resulting distribution of topoisomers is also increased by two with respect to the controls. This effect depends on the presence of an intact HRE and is almost undetectable with the 40-kD form of the receptor. Thus, binding of the hormone receptor to functional DNA regulatory sites located in closed circular plasmids results in a topological change that could be related to the hormonal activation of transcription.