Mechanisms of the inhibition of reverse transcription by unmodified and modified antisense oligonucleotides.

We demonstrated that unmodified and modified (phosphorothioate) oligonucleotides prevent cDNA synthesis by AMV or HIV reverse transcriptases. Antisense oligonucleotide/RNA hybrids specifically arrest primer extension. The blockage involves the degradation of the RNA fragment bound to the antisense oligonucleotide by the reverse transcriptase-associated RNase H activity. However, the phosphorothioate oligomer inhibited polymerization by binding to the AMV RT rather than to the template RNA, whereas there was no competitive binding of the phosphorothioate oligomer on the HIV RT during reverse transcription.