SIGNAL SENSING BY SIGMA(54)-DEPENDENT REGULATORS - DEREPRESSION AS A CONTROL MECHANISM

Transcription by RNA polymerase utilizing the alternative sigma factor sigma(54) is regulated by a distinct class of positive activators des ignated the sigma(54)-dependent family. The activities of these regula tors are themselves modulated in response to a wide variety of environ mental signals. Factors that modulate the expression or the activity o f the regulatory protein in response to chemical and metabolic changes are ultimately responsible for determining the level of expression of sigma(54)-dependent genes and hence the diverse bacterial functions t hat they encode. Many members of the sigma(54)-dependent family are pa rt of two-component sensor-response systems. This MicroReview emphasiz es recent data concerning the activities of a distinct subgroup of the sigma(54)-dependent regulators that directly sense and respond with t ranscriptional activation to the presence of small effector molecules in their environment. The functional consequences of effector activati on in terms of regulation of the enzymatic (ATPase) activity of these transcriptional activators and interdomain interactions are discussed.