The structure-specific endonuclease complex SLX4/XPF regulates Tus/Ter-induced homologous recombination
Abstract Vertebrate replication forks arrested at an interstrand DNA crosslink (ICL) can engage the Fanconi anemia (FA) pathway of ICL repair. The FANCP product, SLX4, binds the FANCQ/XPF/ERCC4-ERCC1 endonuclease, which incises bidirectionally arrested forks to ‘unhook’ the ICL. The resulting double strand break (DSB) is repaired by homologous recombination (HR). Whether this mechanism operates at replication blocks other than ICLs is unknown. Here, we study the role of mammalian SLX4 in HR triggered by a site-specific, chromosomal DNA-protein replication fork barrier formed by the Escherichia coli-derived Tus/Ter complex. We identify an SLX4-XPF-mediated step that is required for Tus/Ter-induced HR but not for HR induced by a replication-independent DSB. We additionally identify a requirement for SLX4-XPF in DSB-induced ‘long tract’ gene conversion, a replicative HR pathway related to break-induced replication. Our work suggests that Tus/Ter-induced HR recapitulates the incision step of replication-coupled ICL repair, and that the full FA mechanism can process DNA-protein barriers for HR.