The regulation of bacterial transcription initiation

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Abstract
The DNA-dependent multi-subunit RNA polymerase is the central component in the regulation of transcription initiation in bacteria. Sigma factors bind to the RNA polymerase to produce a holoenzyme that is competent for transcription. There are multiple factors that determine the level of transcription of a particular gene in a bacterium. The crucial sequence elements of a bacterial promoter are described, including the −35 element, the −10 element, the extended −10 element and the UP element. The role played by sigma factors in bacterial gene regulation is briefly outlined. Small ligands, like ppGpp, can influence the level of transcription of certain genes. Transcription factors can either activate or repress transcription by several mechanisms, but all of these mechanisms involve either optimizing the interaction of the RNA polymerase holoenzyme with the promoter (activation) or preventing the RNA polymerase holoenzyme from binding to the promoter (repression). The organisation of the bacterial chromosome — although still poorly understood — contributes to the regulation of bacterial transcription initiation. Promoters are frequently regulated by changes in environmental or physiological conditions. It is rare for a promoter to be regulated in response to a single environmental or physiological factor. Instead, several signals are often integrated by one (or more) transcriptional regulator by a combination of mechanisms at the promoter.