Abstract
The ς initiation factor ς70 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 λ gene Q protein. Q is able to bind and modify RNAP when α70, 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 rpoD gene for ς70 that impair Q function because they reduce the ability of ς70 to recognize the downstream pause site. These mutations identify a locus of ς70 that is important for the formation and stability of open promoter complex, likely because it mediates protein interactions with RNAP core.