Actinomycin D inhibition of DNA strand transfer reactions catalyzed by HIV-1 reverse transcriptase and nucleocapsid protein.

Actinomycin D was found to be a potent inhibitor of HIV-1 reverse transcriptase catalyzed DNA strand transfer reactions. Using an oligonucleotide model system, actinomycin D inhibition of DNA strand transfer was examined to elucidate the mechanism of inhibition and further define the mechanism of DNA strand transfer. Our results show that actinomycin D inhibits HIV-1 reverse transcriptase catalyzed DNA strand transfer without inhibiting RNA-dependent or DNA-dependent DNA polymerase activity. Actinomycin D was found to strongly inhibit annealing of a primary DNA product to the DNA acceptor template, preventing the formation of a key reaction intermediate. The HIV-1 nucleocapsid protein has been shown to participate in catalytic events during reverse transcription including DNA strand transfer. Recombinant nucleocapsid protein was used in conjunction with actinomycin D in this model system to investigate how NC may participate in the mechanism of inhibition by actinomycin D and in DNA strand transfer. The inclusion of nucleocapsid protein was found to partially relieve both DNA annealing and strand transfer inhibition caused by actinomycin D. This study suggests a potential new mechanism for inhibiting retroviral replication by preventing the formation of replication intermediates.