Half-att site substrates reveal the homology independence and minimal protein requirements for productive synapsis in λ excisive recombination

摘要: Abstract The early events in site-specific excisive recombination were studied with phage λ half- att sites that have no DNA to one side of the strand exchange region; they carry a single core-type integrase binding site and either P or P′ arm flanking DNA. These R L exhibit normal properties for initial (covalent) top-strand transfer form stable intermediates independent later steps reaction. With these novel substrates we show Xis specifically promotes first enhances Int cleavage at R. It is also shown synapsis transfers do not require DNA-DNA pairing but are mediated by protein-protein protein-DNA interactions. involve two (required exchange) and, addition, bottom-strand (C′) responsible second exchange.