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J. Biol. Chem., Vol. 277, Issue 21, 18611-18618, May 24, 2002

This Article Full Text Full Text (PDF) All Versions of this Article: 277/21/18611    most recent M110836200v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rigourd, M. Articles by Marquet, R. Search for Related Content PubMed PubMed Citation Articles by Rigourd, M. Articles by Marquet, R. Social Bookmarking                      What's this?

Primer Unblocking and Rescue of DNA Synthesis by Azidothymidine (AZT)-resistant HIV-1 Reverse Transcriptase
COMPARISON BETWEEN INITIATION AND ELONGATION OF REVERSE TRANSCRIPTION AND BETWEEN () AND (+) STRAND DNA SYNTHESIS^*

Mickaël Rigourd, Chantal Ehresmann, Michael A. Parniak^§¶, Bernard Ehresmann, and Roland Marquet

From the  Unité Propre de Recherche 9002 du CNRS, Institut de Biologie Moléculaire et Cellulaire, 15 rue René Descartes, 67084 Strasbourg cedex, France and the ^§ Jewish General Hospital, Lady Davis Institute for Medical Research, Montréal, Quebec H3T 1E2, Canada

Azidothymidine (AZT) is a widely used inhibitor of type 1 human immunodeficiency virus reverse transcriptase (RT) that acts as chain terminator. Upon treatment, mutations conferring AZT resistance to RT are gradually selected. It has been shown that resistant RT is able to unblock the AZT-terminated primer by an ATP-dependent mechanism. However, this resistance mechanism has only been demonstrated for DNA-dependent DNA elongation. Here, we compared the AZT resistance of mutant RT during DNA elongation on DNA and RNA templates. We showed that, during DNA elongation, primer unblocking and rescue of DNA synthesis take place with similar rate constants on DNA and RNA templates. However, the fraction of a primer eventually repaired during RNA-dependent DNA synthesis is 2× lower compared with that of DNA-dependent synthesis, leading to reduced resistance. We also compared the initiation of reverse transcription, which uses tRNA as a primer and displays characteristic kinetic features, and the subsequent RNA-dependent elongation. Unlike during elongation, resistant RT was unable to unblock the AZT-terminated primer during initiation of () DNA strand synthesis. Our results demonstrate that the efficiency of primer unblocking conferred by the AZT resistance mutations greatly vary during the different steps of the provirus synthesis. These results also suggest that inhibitors specifically targeting the initiation of reverse transcription might prove to be advantageous, as compared with elongation inhibitors.

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