Tuesday, April 8, 2008

DNA supercoiling

Varying levels of positive and negative supercoiling differently affect the efficiency with which topoisomerase II catenates and decatenates DNA

Type II DNA topoisomerases catalyze the transport of one DNA double helix through another. Here, by using a non-hydrolyzable analog of ATP, I examined the single-step DNA transport preferences of the yeast type II topoisomerase bound to positively and negatively supercoiled DNA rings. I found that negative supercoiling favors decatenation of DNA rings more than positive supercoiling. Conversely, positive supercoiling favors the catenation and knotting of DNA rings more than negative supercoiling. This vectorial effect of DNA supercoiling handedness supports a model in which type II topoisomerases can recognize three DNA segments, and highlights a novel influence of DNA supercoiling in global DNA topology.


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