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

The bacteriophage lambda Q protein is a transcription anti-termination factor that controls expression of the phage late genes as a stable component of the transcription elongation complex. To join the elongation complex, lambda Q binds a specific DNA sequence element and interacts with RNA polymerase that is paused during early elongation. lambda Q binds to the paused early-elongation complex through interactions between lambda Q and two regions of RNA polymerase: region 4 of the sigma(70) subunit and the flap region of the beta subunit. We present the 2.1 angstrom resolution crystal structure of a portion of lambda Q containing determinants for interaction with DNA, interaction with region 4 of sigma(70), and interaction with the beta 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 lambda Q alters the functional properties of the transcription elongation complex.