title: The split-end model for homologous recombination at double-strand breaks and at Chi.
abstract: In recent years two different styles of model for homologous recombination have been discussed, depending on whether or not the recombination event occurs in the vicinity of a double-strand break in DNA. The models of Holliday and Meselson and Radding exemplify those that do not involve a break whereas the model of Szostak et al is taken as an example of those that do. Recent advances in understanding a prototypic recombination system thought to promote exchange distant from DNA ends, at Chi sites, suggest a mechanism of initiation neither like Holliday/Meselson-Radding nor like Szostak et al. In those models, only one strand of DNA may invade a homologous DNA molecule. We propose a model for Chi in which exonuclease degrades DNA from a double-strand break to the Chi site; the exonuclease is converted into a helicase upon interaction with Chi; unwinding produces a recombinagenic split-end, and both 3'- and 5'-ending strands at the split-end are capable of invading a homologue. Different genetic consequences are proposed to result from invasion by each. We review evidence supporting the split-end model and suggest its application in at least some cases previously considered to proceed via the Meselson/Radding model and by the double-strand-break repair model of Szostak et al.
authors.affiliation: Department of Genetics, University of Alberta, Edmonton, Canada.
authors.forename: S M
authors.initials: SM
authors.lastname: Rosenberg
authors.forename: P J
authors.initials: PJ
authors.lastname: Hastings
mesh_terms: D004247:DNA / Q000737:chemistry / Q000235:genetics*; D004249:DNA Damage; D004260:DNA Repair; D004926:Escherichia coli / Q000235:genetics*; D008957:Models, Genetic; D011995:Recombination, Genetic
chemical_list: D004247:DNA