A surface of Escherichia coli σ70 required for promoter function and antitermination by phage λ Q protein

The sigma initiation factor sigma(70) of Escherichia coli acts not only in promoter recognition and DNA strand opening, but also to mediate the transformation of RNA polymerase (RNAP) to an antiterminating form by the phage lambda gene Q protein. Q is able to bind and modify RNAP when alpha(70), still present in the initially elongating enzyme, recognizes a repeat of the -10 promoter element and induces a transcription pause. We have isolated mutations in the rgoD gene for sigma(70) that impair Q function because they reduce the ability of sigma(70) to recognize the downstream pause site. These mutations identify a locus of sigma(70) that is important for the formation and stability of open promoter complex, likely because it mediates protein interactions with RNAP core.