The Topological Mechanism of Phage λ Integrase

摘要: Bacteriophage lambda integrase (Int) is a versatile site-specific recombinase. In concert with other proteins, it mediates phage integration into and excision out of the bacterial chromosome. Int recombines intramolecular sites in inverse or direct orientation on separate DNA molecules. This wide spectrum Int-mediated reactions has, however, hindered our understanding topology recombination. By systematically analyzing reaction products using mathematical method called tangles, we deduce unified model for We find that, even absence (-) supercoiling, all are chiral, producing one two possible enantiomers each product. propose that this chirality reflects right-handed crossing within between recombination synaptic complex favors formation Holliday junction intermediates. demonstrate change linking number associated excisive inversion relaxed equally +2 -2, reflecting different substrates but same chirality. Additionally, integrative differs from only by additional plectonemic crossings complex: supercoiled substrates. The generality results indicated finding members superfamily recombinases, Flp yeast Cre P1, show intrinsic as Int.