title: Synapsis and strand exchange in the resolution and DNA inversion reactions catalysed by the beta recombinase.
abstract: In the presence of a sequence-independent chromatin-associated protein, such as Hbsu or HMGB, the beta recombinase catalyses resolution between two directly oriented recombination sites (six sites) and both resolution and DNA inversion between two inversely oriented six sites. Assembly of the synaptic complex requires binding of the beta recombinase to the six sites and the presence of Hbsu. Whether resolution or inversion will take place depends on the relative orientation of the two six sites, the level of DNA supercoiling and the amounts of Hbsu. In this work, the topologies of the products of the resolution and inversion reactions were analysed. The resolution reaction generated mainly singly catenated DNA circles, while DNA inversion gave rise to unknotted circles and small amounts of DNA molecules containing 3- or 5-noded knots. In spite of the distinctive features of the beta system, the topology of synapsis and strand exchange during the resolution reaction is similar to that of Tn3 and gammadelta resolvases. The ability of the beta recombinase to catalyse both inversion and resolution reactions probably reflects different possible architectures of the synaptic complex, which to a large extent depends on Hbsu.
authors.affiliation: Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología, CSIC, Campus de la Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
authors.forename: Inés
authors.initials: I
authors.lastname: Canosa
authors.forename: Gema
authors.initials: G
authors.lastname: López
authors.forename: Fernando
authors.initials: F
authors.lastname: Rojo
authors.forename: Martin R
authors.initials: MR
authors.lastname: Boocock
authors.forename: Juan C
authors.initials: JC
authors.lastname: Alonso
mesh_terms: D001426:Bacterial Proteins; D002384:Catalysis; D007446:Chromosome Inversion; D023902:Chromosome Pairing; D004247:DNA / Q000737:chemistry*; D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D004270:DNA, Circular / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism; D008957:Models, Genetic; D009690:Nucleic Acid Conformation; D045522:Recombinases; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D013573:Synaptonemal Complex
chemical_list: D001426:Bacterial Proteins; D004270:DNA, Circular; D004268:DNA-Binding Proteins; C075779:Hbsu protein, bacteria; D045522:Recombinases; D004247:DNA; D004254:DNA Nucleotidyltransferases