In vitro catenation and decatenation of DNA and a novel eucaryotic ATP-dependent topoisomerase.

Extracts from X. laevis germinal vesicles interlock duplex DNA circles to form catenanes. The catenation activity requires Mg++ and ATP. Negatively supercoiled or relaxed DNA can be used as substrates for the catenation reaction. Homology between donor and acceptor DNA is not required, since catenanes are formed between DNA molecules with unrelated sequences. In the course of the isolation of the activity responsible for the catenation reaction, we discovered a new ATP-dependent topoisomerase. The fractions containing the novel topoisomerase catenate and decatenate DNA, the ionic strength dictating which of the two opposing reactions will occur.