Hormone activation induces nucleosome positioning in vivo

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Abstract
The mouse mammary tumor virus (MMTV) promoter is induced by glucocorticoid hormone. A robust hormone‐ and receptor‐dependent activation could be reproduced in Xenopus laevis oocytes. The homogeneous response in this system allowed a detailed analysis of the transition in chromatin structure following hormone activation. This revealed two novel findings: hormone activation led to the establishment of specific translational positioning of nucleosomes despite the lack of significant positioning in the inactive state; and, in the active promoter, a subnucleosomal particle encompassing the glucocorticoid receptor (GR)‐binding region was detected. The presence of only a single GR‐binding site was sufficient for the structural transition to occur. Both basal promoter elements and ongoing transcription were dispensable. These data reveal a stepwise process in the transcriptional activation by glucocorticoid hormone.