title: Regulation of directionality in bacteriophage lambda site-specific recombination: structure of the Xis protein.
abstract: Upon induction of a bacteriophage lambda lysogen, a site-specific recombination reaction excises the phage genome from the chromosome of its bacterial host. A critical regulator of this process is the phage-encoded excisionase (Xis) protein, which functions both as a DNA architectural factor and by cooperatively recruiting integrase to an adjacent binding site specifically required for excision. Here we present the three-dimensional structure of Xis and the results of a structure-based mutagenesis study to define the molecular basis of its function. Xis adopts an unusual "winged"-helix motif that is modeled to interact with the major- and minor-grooves of its binding site through a single alpha-helix and loop structure ("wing"), respectively. The C-terminal tail of Xis, which is required for cooperative binding with integrase, is unstructured in the absence of DNA. We propose that asymmetric bending of DNA by Xis positions its unstructured C-terminal tail for direct contacts with the N-terminal DNA-binding domain of integrase and that an ensuing disordered to ordered transition of the tail may act to stabilize the formation of the tripartite integrase-Xis-DNA complex required for phage excision.
authors.affiliation: Department of Chemistry and Biochemistry, University of California-Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1570, USA.
authors.forename: My D
authors.initials: MD
authors.lastname: Sam
authors.forename: Christie V
authors.initials: CV
authors.lastname: Papagiannis
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Connolly
authors.forename: Leah
authors.initials: L
authors.lastname: Corselli
authors.forename: Junji
authors.initials: J
authors.lastname: Iwahara
authors.forename: James
authors.initials: J
authors.lastname: Lee
authors.forename: Martin
authors.initials: M
authors.lastname: Phillips
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Wojciak
authors.forename: Reid C
authors.initials: RC
authors.lastname: Johnson
authors.forename: Robert T
authors.initials: RT
authors.lastname: Clubb
mesh_terms: D020816:Amino Acid Motifs; D001287:Attachment Sites, Microbiological; D010582:Bacteriophage lambda / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D004254:DNA Nucleotidyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D019426:Integrases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008957:Models, Genetic; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D011995:Recombination, Genetic; D013329:Structure-Activity Relationship; D014764:Viral Proteins
chemical_list: D011994:Recombinant Proteins; D014764:Viral Proteins; D004254:DNA Nucleotidyltransferases; D019426:Integrases; C063911:excisionase