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Journal of Virology, April 2002, p. 3248-3256, Vol. 76, No. 7
0022-538X/02/$04.00+0     DOI: 10.1128/JVI.76.7.3248-3256.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

The M184V Mutation Reduces the Selective Excision of Zidovudine 5'-Monophosphate (AZTMP) by the Reverse Transcriptase of Human Immunodeficiency Virus Type 1

Paul L. Boyer,1 Stefan G. Sarafianos,2 Edward Arnold,2 and Stephen H. Hughes1*

HIV Drug Resistance Program, National Cancer Institute, Frederick, Maryland 21702-1201,1 Center for Advanced Biotechnology and Medicine and Chemistry Department, Rutgers University, Piscataway, New Jersey 08854-56382

Received 18 October 2001/ Accepted 2 January 2002

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.


* Corresponding author. Mailing address: HIV Drug Resistance Program, National Cancer Institute-FCRDC, P.O. Box B, Building 539, Room 130A, Frederick, MD 21702-1201. Phone: (301) 846-1619. Fax: (301) 846-6966. E-mail: hughes{at}ncifcrf.gov.


Journal of Virology, April 2002, p. 3248-3256, Vol. 76, No. 7
0022-538X/02/$04.00+0     DOI: 10.1128/JVI.76.7.3248-3256.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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