The Escherichia coli cAMP receptor protein (CRP) is a factor that activates transcription at over 100 target promoters. At Class I CRP-dependent promoters, CRP binds immediately upstream of RNA polymerase and activates transcription by making direct contacts with the C-terminal domain of the RNA polymerase α subunit (αCTD). Since αCTD is also known to interact with DNA sequence elements (known as UP elements), we have constructed a series of semi-synthetic Class I CRP-dependent promoters, carrying both a consensus DNA-binding site for CRP and a UP element at different positions. We previously showed that, at these promoters, the CRP–αCTD interaction and the CRP–UP element interaction contribute independently and additively to transcription initiation. In this study, we show that the two halves of the UP element can function independently, and that, in the presence of the UP element, the best location for the DNA site for CRP is position -69.5. This suggests that, at Class I CRP-dependent promoters where the DNA site for CRP is located at position -61.5, the two αCTDs of RNA polymerase are not optimally positioned. Two experiments to test this hypothesis are presented.
The Ada protein is a class I transcription factor of Escherichia coli.
