Regulation of Transcription Factor Activity

We have seen in the preceding discussion how combinations of activators and repressors that bind to specific DNA regulatory sequences control transcription of eukaryotic genes. Whether or not a specific gene in a multicellular organism is expressed in a particular cell at a particular time is largely a consequence of the concentrations and activities of the transcription factors that interact with the regulatory sequences of that gene. Which transcription factors are expressed in a particular cell type, and the amounts produced, is determined by multiple regulatory interactions between transcription-factor genes that occur during the development and differentiation of a particular cell type. In Chapters 15 and 22, we present examples of such regulatory interactions during development and discuss the principles of development and differentiation that have emerged from these examples.

Not only is the expression of transcription factors by a cell regulated, but the activities of those factors expressed in a particular cell type commonly are further controlled

► FIGURE 11-40 Examples of hormones that bind to nuclear receptors. These and related lipid-soluble hormones bind to receptors located in the cytosol or nucleus. The ligand-receptor complex functions as a transcription activator.

Cortisol

Cortisol

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