BglG, the transcriptional antiterminator of the bgl system, interacts with the β′ subunit of the Escherichia coli RNA polymerase

The Escherichia coli BglG protein antiterminates transcription at two terminator sites within the bgl operon in response to the presence of β-glucosides in the growth medium. BglG was previously shown to be an RNA-binding protein that recognizes a specific sequence located just upstream of each of the terminators and partially overlapping with them. We show here that BglG also binds to the E. coli RNA polymerase, both in vivo and in vitro. By using several techniques, we identified the β′ subunit of RNA polymerase as the target for BglG binding. The region that contains the binding site for BglG was mapped to the N-terminal region of β′. The β′ subunit, produced in excess, prevented BglG activity as a transcriptional antiterminator. Possible roles of the interaction between BglG and the polymerase β′ subunit are discussed.