title: Structural basis for the interaction of Escherichia coli NusA with protein N of phage lambda.
abstract: The C terminus of transcription factor NusA from Escherichia coli comprises two repeat units, which bind during antitermination to protein N from phage lambda. To delineate the structural basis of the NusA-lambdaN interaction, we attempted to crystallize the NusA C-terminal repeats in complex with a lambdaN peptide (residues 34-47). The two NusA domains became proteolytically separated during crystallization, and crystals contained two copies of the first repeat unit in contact with a single lambdaN fragment. The NusA modules employ identical regions to contact the peptide but approach the ligand from opposite sides. In contrast to the alpha-helical conformation of the lambdaN N terminus in complex with boxB RNA, residues 34-40 of lambdaN remain extended upon interaction with NusA. Mutational analyses indicated that only one of the observed NusA-lambdaN interaction modes is biologically significant, supporting an equimolar ratio of NusA and lambdaN in antitermination complexes. Solution studies indicated that additional interactions are fostered by the second NusA repeat unit, consistent with known compensatory mutations in NusA and lambdaN. Contrary to the RNA polymerase alpha subunit, lambdaN binding does not stimulate RNA interaction of NusA. The results demonstrate that lambdaN serves as a scaffold to closely oppose NusA and the mRNA in antitermination complexes.
authors.affiliation: Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Am Klopferspitz 18a, D-82152 Martinsried, Germany.
authors.forename: Irena
authors.initials: I
authors.lastname: Bonin
authors.forename: Rene
authors.initials: R
authors.lastname: Mühlberger
authors.forename: Gleb P
authors.initials: GP
authors.lastname: Bourenkov
authors.forename: Robert
authors.initials: R
authors.lastname: Huber
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.forename: Gerald
authors.initials: G
authors.lastname: Richter
authors.forename: Markus C
authors.initials: MC
authors.lastname: Wahl
mesh_terms: D000595:Amino Acid Sequence; D010582:Bacteriophage lambda / Q000378:metabolism*; D001665:Binding Sites; D002151:Calorimetry; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019590:Nucleocapsid Proteins / Q000737:chemistry* / Q000378:metabolism*; D010445:Peptide Elongation Factors / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D013816:Thermodynamics; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D035602:Transcriptional Elongation Factors
chemical_list: D029968:Escherichia coli Proteins; D019590:Nucleocapsid Proteins; D010445:Peptide Elongation Factors; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; C068727:nusA protein, E coli