A model for hormone receptor binding to the mouse mammary tumour virus regulatory element based on hydroxyl radical footprinting.

The mouse mammary tumour virus long terminal repeat region contains regulatory sequences able to mediate transcriptional induction by different steroid hormones. Two clusters of binding sites for the glucocorticoid and the progesterone receptors have been identified in the region between -70 and -190, the so called hormone responsive or regulatory element. To understand the molecular details of the interaction between the receptors and the DNA we have used the high resolution technique of hydroxyl radical footprinting. Both in the promoter distal site and in the promoter proximal cluster additional contacts between the proteins and the double helix are detected by this technique, outside of the region identified by methylation protection. The pattern of contacts in the promoter distal region is compatible with a model involving the interaction of a receptor dimer with the major grooves of four subsequent turns of the double helix, each turn being contacted by a separate zinc finger. This model is illustrated by computer graphical methods and discussed in terms of sequence homologies with other hormone regulatory elements.