Xis protein binding to the left arm stimulates excision of conjugative transposon Tn916.
Tn916 and related conjugative transposons are clinically significant vectors for the transfer of antibiotic resistance among human pathogens, and they excise from their donor organisms using the transposon-encoded integrase ((Tn916)Int) and excisionase ((Tn916)Xis) proteins. In this study, we have investigated the role of the (Tn916)Xis protein in stimulating excisive recombination. The functional relevance of (Tn916)Xis binding sites on the arms of the transposon has been assessed in vivo using a transposon excision assay. Our results indicate that in Escherichia coli the stimulatory effect of the (Tn916)Xis protein is mediated by sequence-specific binding to either of its two binding sites on the left arm of the transposon. These sites lie in between the core and arm sites recognized by (Tn916)Int, suggesting that the (Tn916)Xis protein enhances excision in a manner similar to the excisionase protein of bacteriophage lambda, serving an architectural role in the stabilization of protein-nucleic acid structures required for strand synapsis. However, our finding that excision in E. coli is significantly enhanced by the host factor HU, but does not depend on the integration host factor or the factor for inversion stimulation, defines clear mechanistic differences between Tn916 and bacteriophage lambda recombination.
Connolly
Kevin M
KM
Department of Chemistry and Biochemistry, UCLA-DOE Laboratory of Structural Biology and Molecular Medicine, and the Molecular Biology Institute, University of California, Los Angeles, Los Angeles, California 90095-1570, USA.
Iwahara
Mizuho
M
Clubb
Robert T
RT
D001426:Bacterial Proteins / Q000502:physiology; D001483:Base Sequence; D001665:Binding Sites; D003227:Conjugation, Genetic; D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D004251:DNA Transposable Elements / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D034982:Integration Host Factors; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D014764:Viral Proteins
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D034982:Integration Host Factors; D014764:Viral Proteins; D004254:DNA Nucleotidyltransferases; C063911:excisionase