The PspA Protein of Escherichia coli Is a Negative Regulator of ς 54 -Dependent Transcription

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Abstract
In Eubacteria , expression of genes transcribed by an RNA polymerase holoenzyme containing the alternate sigma factor ς 54 is positively regulated by proteins belonging to the family of enhancer-binding proteins (EBPs). These proteins bind to upstream activation sequences and are required for the initiation of transcription at the ς 54 -dependent promoters. They are typically inactive until modified in their N-terminal regulatory domain either by specific phosphorylation or by the binding of a small effector molecule. EBPs lacking this domain, such as the PspF activator of the ς 54 -dependent pspA promoter, are constitutively active. We describe here the in vivo and in vitro properties of the PspA protein of Escherichia coli , which negatively regulates expression of the pspA promoter without binding DNA directly.