Identification of the λ integrase surface that interacts with Xis reveals a residue that is also critical for Int dimer formation
- David Warren*,†,
- My D. Sam†,‡,
- Kate Manley*,†,
- Dibyendu Sarkar§,
- Sang Yeol Lee*,
- Mohamad Abbani‡,
- Jonathan M. Wojciak‡,
- Robert T. Clubb‡,¶, and
- Arthur Landy*,¶
- *Division of Biology and Medicine, Brown University, Providence, RI 02912; ‡Department of Chemistry and Biochemistry, Molecular Biology Institute, University of California, and UCLA–DOE Institute for Genomics and Proteomics, 405 Hilgard Avenue, Los Angeles, CA 90095; and §Institute of Microbial Technology, Sector 39A, Chandigarh 160036, India
-
Contributed by Arthur Landy, May 20, 2003
Abstract
Lambda integrase (Int) is a heterobivalent DNA-binding protein that together with the accessory DNA-bending proteins IHF, Fis, and Xis, forms the higher-order protein–DNA complexes that execute integrative and excisive recombination at specific loci on the chromosomes of phage λ and its Escherichia coli host. The large carboxyl-terminal domain of Int is responsible for binding to core-type DNA sites and catalysis of DNA cleavage and ligation reactions. The small amino-terminal domain (residues 1–70), which specifies binding to arm-type DNA sites distant from the regions of strand exchange, consists of a three-stranded β-sheet, proposed to recognize the cognate DNA site, and an α-helix. We report here that a site on this α-helix is critical for both homomeric interactions between Int protomers and heteromeric interactions with Xis. The mutant E47A, which was identified by alanine-scanning mutagenesis, abolishes interactions between Int and Xis bound at adjacent binding sites and reduces interactions between Int protomers bound at adjacent arm-type sites. Concomitantly, this residue is essential for excisive recombination and contributes to the efficiency of the integrative reaction. NMR titration data with a peptide corresponding to Xis residues 57–69 strongly suggest that the carboxyl-terminal tail of Xis and the α-helix of the aminoterminal domain of Int comprise the primary interaction surface for these two proteins. The use of a common site on λ Int for both homotypic and heterotypic interactions fits well with the complex regulatory patterns associated with this site-specific recombination reaction.
