Both HIV-1 reverse transcriptase (RT) and topoisomerase I bind to structural RNAs and they cooperate to synthesize cDNA during the replication of HIV-1. In this study, we find that human topoisomerase I exclusively dissociated HIV-1 reverse transcriptase, which strongly binds to structural RNAs. Meanwhile, topoisomerase I did not dissociate either HIV-1 nucleocapsid proteins or murine leukemia virus RT which was bound to RNA. We propose that human topoisomerase I may regulate the binding of RT to RNAs and play a pivotal role in HIV-1 replication. (C) 2003 Elsevier Inc. All rights reserved.