Mammary Tumor Virus DNA: A Glucocorticoid-responsive Transposable Element

Abstract

Steroid hormones exert profound and specific effects on patterns of gene expression in virtually all metazoan organisms. In mammalian and avian tissues, where the biochemistry of the action of these hormones has been most extensively studied, the “interpretation” of the chemical structure of the steroid seems to be mediated by soluble receptor molecules; these proteins bind the appropriate hormone specifically and with high affinity and thereby initiate a process that results in the appearance of a specific set of new gene products. In effect, the steroid acts as an allosteric ligand; that is, the binding event somehow alters the properties of the receptor so as to increase its affinity for binding sites in the cell nucleus, resulting in a net translocation of the steroid-receptor complex from the soluble to the nuclear bound state. The interaction with components of the chromatin is then presumed to bring about the biological response (for...