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

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 et subunits, or containing one full-length alpha subunit and one truncated alpha subunit lacking the alpha C-terminal domain (alphaCTD). At a promoter having a single DNA site for CRP, activation requires only one full-length ut subunit. Likewise, at a promoter having a single DNA site for CRP and one adjacent UP-element subsite (high-affinity DNA site for alphaCTD), activation requires only one full-length at 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 (alpha subunits. We conclude that a single copy of alphaCTD is sufficient to interact with one CRP molecule and one adjacent UP-element subsite, but two copies of aCTD are required to interact with two CRP molecules or with one CRP molecule and two UP-element subsites.