BEHAVIOR OF A CROSS-LINKED ATTACHMENT SITE - TESTING THE ROLE OF BRANCH MIGRATION IN SITE-SPECIFIC RECOMBINATION

Integrative recombination of bacteriophage lambda requires perfect homology between partners over a short segment of DNA, the overlap region, that separates the positions of top and bottom strand exchange. We constructed a specific cross-link between complementary strands in the overlap region of one partner, using a method designed to introduce minimal distortion of DNA. The modified attachment site could initiate recombination, forming a Holliday junction, but could not resolve this junction so as to complete the recombination. This demonstrates that the ability of complementary base-pairs to dissociate is important for overlap region function and strongly supports the view that branch migration across this region is the way homology is sensed during integrative recombination. © 1991.