The PspA protein of Escherichia coli is a negative regulator of sigma(54)-dependent transcription

In Eubacteria, expression of genes transcribed by an RNA polymerase holoenz yme containing the alternate sigma factor sigma(54) is positively regulated by proteins belonging to the family of enhancer-binding proteins (EBPs), T hese proteins bind to upstream activation sequences and are required for th e initiation of transcription at the sigma(54)-dependent promoters. They ar e typically inactive until modified in their N-terminal regulatory domain e ither by specific phosphorylation or by the binding of a small effector mol ecule. EBPs lacking this domain, such as the PspF activator of the sigma(54 )-dependent pspA promoter, are constitutively active. We describe here the in vivo and in vitro properties of the PspA protein of Escherichia coli, wh ich negatively regulates expression of the pspA promoter without binding DN A directly.