SUMMARY
The bacteriophage λ Q protein is a transcription antitermination factor that controls expression of the phage late genes as a stable component of the transcription elongation complex. To join the elongation complex, λQ binds a specific DNA sequence element and interacts with RNA polymerase that is paused during early elongation. λQ’s interaction with the paused early elongation complex involves interactions between λQ and two regions of RNA polymerase: region 4 of the σ70 subunit and the flap domain of the β subunit. We present the 2.1 Å resolution crystal structure of a portion of λQ containing determinants for interaction with DNA, interaction with region 4 of σ70, and interaction with the β flap. The structure provides a framework for interpreting prior genetic and biochemical analysis and sets the stage for future structural studies to elucidate the mechanism by which λQ alters the functional properties of the transcription elongation complex.
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