Chromatin Template Remodeling and Steroid Receptor Transactivation of MMTV
The major current paradigm for our understanding of transcriptional regulation in eukaryotic cells is delineated within a set of concepts that are generally referred to as the protein-protein, or looping model. Under this view (Fig. 1), the proteins involved in gene activation, or repression, at a given locus are thought to interact cooperatively with each other in such a way that the stability of a given activating (or repressing) complex is initiated and maintained by direct contacts between the various members of the multifactorial group. The absence of one member of the complex would lower the affinity sufficiently to establish an equilibrium condition with the complex dissociated from the DNA regulatory sequence, and control of the target promoter would thus be exerted. According to this model, the primary function of DNA is simply to organize recognition sites for the various regulatory proteins in such a way that kinetically favorable protein-protein interactions can occur. That is, the DNA serves as a two-dimensional “string,” assembling recognition sites for the appropriate factors in space so that the local concentration exceeds that required to facilitate assembly of the initiating complex.
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