RESUMEN
Integrases, such as that of the Streptomyces temperate bacteriophage ÏC31, promote site-specific recombination between DNA sequences in the bacteriophage and bacterial genomes to integrate or excise the phage DNA. ÏC31 integrase belongs to the serine recombinase family, a large group of structurally related enzymes with diverse biological functions. It has been proposed that serine integrases use a "subunit rotation" mechanism to exchange DNA strands after double-strand DNA cleavage at the two recombining att sites, and that many rounds of subunit rotation can occur before the strands are religated. We have analyzed the mechanism of ÏC31 integrase-mediated recombination in a topologically constrained experimental system using hybrid "phes" recombination sites, each of which comprises a ÏC31 att site positioned adjacent to a regulatory sequence recognized by Tn3 resolvase. The topologies of reaction products from circular substrates containing two phes sites support a right-handed subunit rotation mechanism for catalysis of both integrative and excisive recombination. Strand exchange usually terminates after a single round of 180° rotation. However, multiple processive "360° rotation" rounds of strand exchange can be observed, if the recombining sites have nonidentical base pairs at their centers. We propose that a regulatory "gating" mechanism normally blocks multiple rounds of strand exchange and triggers product release after a single round.
Asunto(s)
Bacteriófagos/enzimología , Integrasas/metabolismo , Recombinación Genética , Bacteriófagos/genética , ADN Viral/genética , Integrasas/genéticaRESUMEN
The Topological Aspects of DNA Function and Protein Folding international meeting provided an interdisciplinary forum for biological scientists, physicists and mathematicians to discuss recent developments in the application of topology to the study of DNA and protein structure. It had 111 invited participants, 48 talks and 21 posters. The present article discusses the importance of topology and introduces the articles from the meeting's speakers.