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Holliday junction affinity of the base excision repair factor Endo III contributes to cholera toxin phage integration
Author(s) -
Bischerour Julien,
Spangenberg Claudia,
Barre FrançoisXavier
Publication year - 2012
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/emboj.2012.219
Subject(s) - biology , cholera toxin , holliday junction , toxin , vibrio cholerae , virology , microbiology and biotechnology , genetics , dna , homologous recombination , bacteria
Toxigenic conversion of Vibrio cholerae bacteria results from the integration of a filamentous phage, CTXφ. Integration is driven by the bacterial Xer recombinases, which catalyse the exchange of a single pair of strands between the phage single‐stranded DNA and the host double‐stranded DNA genomes; replication is thought to convert the resulting pseudo‐Holliday junction (HJ) intermediate into the final recombination product. The natural tendency of the Xer recombinases to recycle HJ intermediates back into substrate should thwart this integration strategy, which prompted a search for additional co‐factors aiding directionality of the process. Here, we show that Endo III, a ubiquitous base excision repair enzyme, facilitates CTXφ‐integration in vivo . In vitro , we show that it prevents futile Xer recombination cycles by impeding new rounds of strand exchanges once the pseudo‐HJ is formed. We further demonstrate that this activity relies on the unexpected ability of Endo III to bind to HJs even in the absence of the recombinases. These results explain how tandem copies of the phage genome can be created, which is crucial for subsequent virion production.