Structure of the DNA-Binding and RNA-Polymerase-Binding Region of Transcription Antitermination Factor λQ

• A 2.1 Å crystal structure of a domain of λQ transcription antiterminator is presented
• The domain mediates interactions with DNA, RNA polymerase, and initiation factor σ70
• The domain comprises a four-helix bundle, zinc binding site, and arm-like structure
• Structure provides insight into λQ’s interactions with DNA, RNA polymerase, and σ70

SummaryThe 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 binds to the paused early-elongation complex through interactions between λQ and two regions of RNA polymerase: region 4 of the σ70 subunit and the flap region 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.