Membrane-mediated Regulation of Gene Expression in Bacteria

Abstract

The final step in the regulation of gene expression in prokaryotes is a cytoplasmic event, since transcription and translation occur inside the cells and there is no nuclear membrane. Most examples of genetic regulation involve effector molecules which, after transport from the outside, are sensed inside the cell by soluble cytoplasmic regulatory proteins. However, a number of exceptions to this totally internal and soluble scheme are known in which membrane proteins participate in gene regulation. In certain cases, membranes can participate in regulation in response to effectors in the cytoplasm when one of the regulatory proteins is membrane-bound rather than free. Alternatively, regulation by a membrane protein that spans the cytoplasmic membrane can occur when the external concentration of an effector molecule is sensed to produce an intracellular regulatory signal. Sensing external effector is one way of controlling genes by a compound in the medium, where that compound is also a metabolic intermediate always present in the cell. External sensing of effectors occurs in many chemotactic responses of bacteria, a subject reviewed by Hazelbauer and Parkinson (this volume). Membranes have also been implicated where regulation is in response to water activity as reflected by osmotic forces. In one example, the osmotic pressure of the medium is sensed; in another, it is the turgor pressure, the difference in osmotic pressure between the inside and outside of the cell, that controls expression.

MEMBRANE PROTEINS AS INTERNAL REGULATORY SENSORS
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