Bacterial enhancer-binding proteins: unlocking σ54-dependent gene transcription

Bacterial transcription relies on the binding of dissociable sigma (σ) factors to RNA polymerase (RNAP) for promoter specificity. The major variant sigma factor (σ54) forms a stable closed complex with RNAP bound to DNA that rarely spontaneously isomerises to an open complex. ATP hydrolysis by bacterial enhancer-binding proteins is used to remodel the RNAP–σ54–DNA closed complex. Recently, a wealth of structural information on bacterial enhancer-binding proteins has enabled unprecedented insights into their mechanism. These data provide a structural basis for nucleotide binding and hydrolysis, oligomerisation and the conversion of ATPase activity into remodelling events within the RNAP–σ54 closed complex, and represent advances towards a complete understanding of the σ54-dependent transcription activation mechanism.