Requirement for two copies of RNA polymerase α subunit C-terminal domain for synergistic transcription activation at complex bacterial promoters

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Abstract
Transcription activation by the Escherichia coli cyclic AMP receptor protein (CRP) at different promoters has been studied using RNA polymerase holoenzyme derivatives containing two full-length α subunits, or containing one full-length α subunit and one truncated α subunit lacking the α C-terminal domain (αCTD). At a promoter having a single DNA site for CRP, activation requires only one full-length α subunit. Likewise, at a promoter having a single DNA site for CRP and one adjacent UP-element subsite (high-affinity DNA site for αCTD), activation requires only one full-length α subunit. In contrast, at promoters having two DNA sites for CRP, or one DNA site for CRP and two UP-element subsites, activation requires two full-length α subunits. We conclude that a single copy of αCTD is sufficient to interact with one CRP molecule and one adjacent UP-element subsite, but two copies of αCTD are required to interact with two CRP molecules or with one CRP molecule and two UP-element subsites.

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