Mechanism by which phosphonoformic acid resistance mutations restore 3'-azido-3'-deoxythymidine (AZT) sensitivity to AZT-resistant HIV-1 reverse transcriptase

J Biol Chem. 2000 Mar 31;275(13):9251-5. doi: 10.1074/jbc.275.13.9251.


The development of phosphonoformic acid (PFA) resistance against a background of 3'-azido-3'-deoxythymidine (AZT) resistance in human immunodeficiency virus type 1 (HIV-1) restores viral sensitivity to AZT. High level AZT resistance requires multiple mutations (D67N/K70R/T215F/K219Q). In order to characterize the mechanism of PFA resistance-mediated resensitization to AZT, the A114S mutation associated with PFA resistance was introduced into the reverse transcriptase (RT) of both wild type and drug-resistant virus. We previously showed that pyrophosphorolytic removal of chain-terminating AZT is the primary mechanism of the AZT resistance phenotype (Arion, D., Kaushik, N., McCormick, S., Borkow, G., and Parniak, M. A. (1998) Biochemistry 37, 15908-15917). Introduction of A114S into the AZT resistance background significantly diminishes both the enhanced pyrophosphorolytic activity and the DNA synthesis processivity associated with the AZT-resistant RT. The A114S mutation also alters the nucleotide-dependent phosphorolysis activity associated with AZT resistance. The presence of the A114S mutation therefore severely impairs the mutant enzyme's ability to excise chain-terminating AZT. The decrease in phosphorolytic activity of RT conferred by the PFA resistance A114S mutation resensitizes AZT-resistant HIV-1 to AZT by allowing the latter to again function as a chain terminator of viral DNA synthesis. These data further underscore the importance of phosphorolytic removal of chain-terminating AZT as the primary mechanism of HIV-1 AZT resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-HIV Agents / pharmacology
  • Base Sequence
  • DNA Primers
  • DNA Replication
  • Drug Resistance, Microbial / genetics
  • Foscarnet / pharmacology*
  • HIV Reverse Transcriptase / drug effects*
  • HIV-1 / drug effects
  • HIV-1 / enzymology
  • HIV-1 / genetics
  • Mutation*
  • Recombinant Proteins / drug effects
  • Reverse Transcriptase Inhibitors / pharmacology*
  • Zidovudine / pharmacology*


  • Anti-HIV Agents
  • DNA Primers
  • Recombinant Proteins
  • Reverse Transcriptase Inhibitors
  • Foscarnet
  • Zidovudine
  • HIV Reverse Transcriptase