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Journal of Bacteriology, February 2000, p. 1024-1034, Vol. 182, No. 4
Department of Biology and Molecular Biology
Institute, San Diego State University, San Diego, California
92182-4614
Received 19 April 1999/Accepted 25 October 1999
Bacteriophage lambda integrase (Int) catalyzes at least four
site-specific recombination pathways between pairs of attachment (att) sites. Protein-protein contacts between monomers of
Int are presumed to be important for these site-specific recombination events for several reasons: Int binds to the att sites
cooperatively, catalytic Int mutants can complement each other for
strand cleavage, and crystal structures for two other recombinases in
the Int family (Cre from phage P1 and Int from Haemophilus
influenzae phage HP1) show extensive protein-protein
contacts between monomers. We have begun to investigate interactions
between Int monomers by three approaches. First, using a genetic assay,
we show that regions of protein-protein interactions occur throughout
Int, including in the amino-terminal domain. This domain was previously
thought to be important only for high-affinity protein-DNA
interactions. Second, we have found that an amino-terminal His tag
reduces cooperative binding to DNA. This disruption in cooperativity
decreases the stable interaction of Int with core sites, where
catalysis occurs. Third, using protein-protein cross-linking to
investigate the multimerization of Int during recombination,
we show that Int predominantly forms dimers, trimers, and tetramers.
Moreover, we show that the cysteine at position 25 is present at or
near the interface between monomers that is involved in the formation of dimers and tetramers. Our evidence indicates that the amino-terminal domain of Int is involved in protein-protein interactions that are
likely to be important for recombination.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Amino Terminus of Bacteriophage
Integrase
Is Involved in Protein-Protein Interactions during
Recombination
*
Corresponding author. Mailing address: Dept. of
Biology and Molecular Biology Institute, San Diego State University,
San Diego, CA 92182-4614. Phone: (619) 594-4490. Fax: (619)
594-5676. E-mail: asegall{at}sunstroke.sdsu.edu.
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