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

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.