The formation of triple-stranded DNA prevents spontaneous branch-migration.
Branch-migration is a fundamental step in the process of DNA recombination that determines the location, and extent, of the exchange between the recombining duplexes. Four-way Holliday junctions assembled in vitro can migrate spontaneously in an uncatalysed reaction that mimics some of the aspects involved in branch-migration. Here, we have analysed the effects of a d(GA.TC)22 and a d(CA.TG)30 sequence on the rate of spontaneous branch-migration. Under most of the experimental conditions assayed, no significant effect was observed. However, the d(GA.TC)22 sequence induces a very strong arrest when branch-migration is performed at low pH, under conditions where the repeated sequence is forming an intramolecular [C(+)T(GA.TC)] triplex. A similar arrest is observed when the recombining duplexes contain intermolecular triplexes arising from the annealing of a d(GA.TC)22 duplex and a d(TC)22 oligonucleotide, indicating that the formation of triplex DNA constitutes a strong barrier for the progression of the Holliday junction. These results are discussed in the context of the possible contribution of triplex DNA to DNA recombination.
Benet
A
A
Centre d'Investigació i Desenvolupament, Institut de Biologia Molecular de Barcelona, CSIC, Jordi Girona Salgado 18-26, Barcelona, 08034, Spain.
Azorín
F
F
D001483:Base Sequence; D004247:DNA / Q000737:chemistry* / Q000235:genetics*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011995:Recombination, Genetic
D004247:DNA