2′-fluoro-modified pyrimidines enhance affinity of RNA oligonucleotides to HIV-1 reverse transcriptase

Nucleic acid aptamers can be chemically modified to enhance function, but modifying previously selected aptamers can have nontrivial structural and functional consequences. We present a reselection strategy to evaluate the impact of several modifications on preexisting aptamer pools. RNA aptamer libraries with affinity to HIV-1 reverse transcriptase (RT) were retranscribed with 2′-F, 2′-OMe, or 2′-NH(2) pyrimidines and subjected to three additional selection cycles. RT inhibition was observed for representative aptamers from several structural families identified by high-throughput sequencing when transcribed with their corresponding modifications. Thus, reselection identified specialized subsets of aptamers that tolerated chemical modifications from unmodified preenriched libraries. Inhibition was the strongest with the 2′-F-pyrimidine (2′-FY) RNAs, as compared to inhibition by the 2′-OMeY and 2′-NH(2)Y RNAs. Unexpectedly, a diverse panel of retroviral RTs were strongly inhibited by all 2′-FY-modified transcripts, including sequences that do not inhibit those RTs as unmodified RNA. The magnitude of promiscuous RT inhibition was proportional to mole fraction 2′-FY in the transcript. RT binding affinity by 2′-FY transcripts was more sensitive to salt concentration than binding by unmodified transcripts, indicating that interaction with retroviral RTs is more ionic in character for 2′-FY RNA than for unmodified 2′-OH RNA. These surprising features of 2′-FY-modified RNA may have general implications for applied aptamer technologies.