Hormonal Regulation of Gene Transcription
This chapter attempts to critically evaluate studies on endogenous and solubilized RNA polymerase activities in isolated nuclei, on transcription of chromatin templates by exogenous enzymes, and on the effects of hormone-receptor complexes on RNA synthesis in vitro. Hormones cause marked proliferation of the protein synthetic apparatus in target cells, an effect which is manifest in terms of increased levels of ribosomes, tRNA, messenger RNA (mRNA), and membranes in the cytoplasm and enhanced rates of initiation of translation. In the presence of estrogen, four mRNA frequency classes are apparent and peak 4 is predominantly ovalbumin (Ov) mRNA. Mercurated RNA (Hg-RNA) transcripts were synthesized in oviduct or spleen nuclei, and the fraction of Ov gene copies was determined in hybridization reactions containing filters to which pOV plasmid DNA was affixed. The chapter discusses two relevant models: one to account for data describing "fine control" and multihormonal control of specific gene transcription, and the second, a working model for steroid action in general.