title: The M184V mutation reduces the selective excision of zidovudine 5'-monophosphate (AZTMP) by the reverse transcriptase of human immunodeficiency virus type 1.
abstract: The M184V mutation in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) causes resistance to lamivudine, but it also increases the sensitivity of the virus to zidovudine (3'-azido-3'-deoxythymidine; AZT). This sensitization to AZT is seen both in the presence and the absence of the mutations that confer resistance to AZT. AZT resistance is due to enhanced excision of AZT 5'-monophosphate (AZTMP) from the end of the primer by the RT of the resistant virus. Published data suggest that the excision reaction involves pyrophosphorolysis but that the likely in vivo pyrophosphate donor is not pyrophosphate but ATP. The mutations that lead to AZT resistance enhance ATP binding and, in so doing, enhance pyrophosphorolysis. The excision reaction is specific for AZT because HIV-1 RT, which can form a closed complex with a dideoxy-terminated primer and an incoming deoxynucleoside triphosphate (dNTP), does not form the closed complex with an AZTMP-terminated primer and an incoming dNTP. This means that an AZTMP-terminated primer has better access to the site where it can be excised. The M184V mutation alters the polymerase active site in a fashion that specifically interferes with ATP-mediated excision of AZTMP from the end of the primer strand. The M184V mutation does not affect the incorporation of AZT 5'-triphosphate (AZTTP), either in the presence or the absence of mutations that enhance AZTMP excision. However, in the presence of ATP, the M184V mutation does decrease the ability of HIV-1 RT to carry out AZTMP excision. Based on these results, and on the results of other excision experiments, we present a model to explain how the M184V mutation affects AZTMP excision.
authors.affiliation: HIV Drug Resistance Program, National Cancer Institute, Frederick, Maryland 21702-1201, USA.
authors.forename: Paul L
authors.initials: PL
authors.lastname: Boyer
authors.forename: Stefan G
authors.initials: SG
authors.lastname: Sarafianos
authors.forename: Edward
authors.initials: E
authors.lastname: Arnold
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Hughes
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D054306:Dideoxynucleotides; D024882:Drug Resistance, Viral; D054303:HIV Reverse Transcriptase / Q000235:genetics* / Q000378:metabolism; D015497:HIV-1 / Q000187:drug effects* / Q000201:enzymology; D009154:Mutation; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology; D013942:Thymine Nucleotides / Q000378:metabolism*; D015215:Zidovudine / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D054306:Dideoxynucleotides; D018894:Reverse Transcriptase Inhibitors; D013942:Thymine Nucleotides; C057287:3'-azido-3'-deoxythymidine 5'phosphate; D015215:Zidovudine; D000255:Adenosine Triphosphate; D054303:HIV Reverse Transcriptase