THE ROLE OF SUPERCOILING IN MYCOBACTERIOPHAGE L5 INTEGRATIVE RECOMBINATION

The genome of temperate mycobacteriophage L5 integrates into the chrom osomes of its hosts, including Mycobacterium smegmatis, Mycobacterium tuberculosis and bacille Calmette-Guerin. This integrase-mediated site -specific recombination reaction occurs between the phage attP site an d the mycobacterial affB site and requires the mycobacterial integrati on host factor. Here we examine the role of supercoiling in this react ion and show that integration is stimulated by DNA supercoiling but th at supercoiling of either the attP or the attB substrate enhances reco mbination. Supercoiling thus facilitates a postsynaptic recombination event. We also show that, while supercoiling is not required for the p roduction of a recombinagenic intasome, a mutant attP DNA deficient in binding of the host factor acquires a dependence on supercoiling for intasome formation and recombination.