Regulation of directionality in bacteriophage λ site-specific recombination: Structure of the Xis protein

My D. Sam, Christie V. Papagiannis, Kevin M. Connolly, Leah Corselli, Junji Iwahara, James Lee, Martin Phillips, Jonathan M. Wojciak, Reid C. Johnson, Robert T. Clubb

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


Upon induction of a bacteriophage λ 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 α-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.

Original languageEnglish (US)
Pages (from-to)791-805
Number of pages15
JournalJournal of Molecular Biology
Issue number4
StatePublished - 2002
Externally publishedYes


  • NMR
  • Phage excision
  • Protein-DNA interactions
  • Site-specific DNA recombination
  • Structure

ASJC Scopus subject areas

  • Molecular Biology
  • Biophysics
  • Structural Biology


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