Recombinogenic flap ligation pathway for intrinsic repair of topoisomerase IB-induced double-strand breaks.
Topoisomerase IB catalyzes recombinogenic DNA strand transfer reactions in vitro and in vivo. Here we characterize a new pathway of topoisomerase-mediated DNA ligation in vitro (flap ligation) in which vaccinia virus topoisomerase bound to a blunt-end DNA joins the covalently held strand to a 5' resected end of a duplex DNA containing a 3' tail. The joining reaction occurs with high efficiency when the sequence of the 3' tail is complementary to that of the scissile strand immediately 5' of the cleavage site. A 6-nucleotide segment of complementarity suffices for efficient flap ligation. Invasion of the flap into the duplex apparently occurs while topoisomerase remains bound to DNA, thereby implying a conformational flexibility of the topoisomerase clamp around the DNA target site. The 3' flap acceptor DNA mimics a processed end in the double-strand-break-repair recombination pathway. Our findings suggest that topoisomerase-induced breaks may be rectified by flap ligation, with ensuing genomic deletions or translocations.
Cheng
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Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA.
Shuman
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D020029:Base Pairing; D001483:Base Sequence; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D017353:Gene Deletion; D007700:Kinetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D011995:Recombination, Genetic; D013997:Time Factors; D014178:Translocation, Genetic; D014616:Vaccinia virus / Q000201:enzymology / Q000235:genetics
D004247:DNA; D004264:DNA Topoisomerases, Type I