Topoisomerase inhibitors can selectively interfere with different stages of simian virus 40 DNA replication.

I have found that type I and type II topoisomerase inhibitors have pronounced but very different effects on SV40 DNA replication. Type II topoisomerase inhibitors selectively interfere with separation of newly replicated SV40 daughter chromosomes, while the type I topoisomerase inhibitor camptothecin rapidly produces broken replication forks in growing Cairns structures. Camptothecin also produces abnormal SV40 DNAs which appear to be intermediates and end products of sister chromatid exchange.