title: Intracellular substrates for the primer-unblocking reaction by human immunodeficiency virus type 1 reverse transcriptase: detection and quantitation in extracts from quiescent- and activated-lymphocyte subpopulations.
abstract: Treatment of human immunodeficiency virus type 1 (HIV-1)-infected patients with 3'-azido-3'-deoxythymidine (AZT) selects for mutant forms of viral reverse transcriptase (RT) with increased ability to remove chain-terminating nucleotides from blocked DNA chains. We tested various cell extracts for the presence of endogenous acceptor substrates for this reaction. Cell extracts incubated with HIV-1 RT and [(32)P]ddAMP-terminated DNA primer/template gave rise to (32)P-labeled adenosine 2',3'-dideoxyadenosine 5',5'''-P(1),P(4)-tetraphosphate (Ap(4)ddA), ddATP, Gp(4)ddA, and Ap(3)ddA, corresponding to the transfer of [(32)P]ddAMP to ATP, PP(i), GTP, and ADP, respectively. Incubation with [(32)P]AZT monophosphate (AZTMP)-terminated primer/template gave rise to the analogous (32)P-labeled AZT derivatives. Based on the rates of formation of the specific excision products, ATP and PP(i) levels were determined: ATP was present at 1.3 to 2.2 mM in H9 cells, macrophages, and unstimulated CD4(+) or CD8(+) T cells, while PP(i) was present at 7 to 15 microM. Under these conditions, the ATP-dependent reaction predominated, and excision by the AZT-resistant mutant RT was more efficient than wild type RT. Activated CD4(+) or CD8(+) T cells contained 1.4 to 2.7 mM ATP and 55 to 79 microM PP(i). These cellular PP(i) concentrations are lower than previously reported; nonetheless, the PP(i)-dependent reaction predominated in extracts from activated T cells, and excision by mutant and wild-type RT occurred with similar efficiency. While PP(i)-dependent excision may contribute to AZT resistance in vivo, it is likely that selection of AZT-resistant mutants occurs primarily in an environment where the ATP-dependent reaction predominates.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, P.O. Box 016129, Miami, FL 33101-6129, USA.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Smith
authors.forename: Peter R
authors.initials: PR
authors.lastname: Meyer
authors.forename: Deshratn
authors.initials: D
authors.lastname: Asthana
authors.forename: Margarita R
authors.initials: MR
authors.lastname: Ashman
authors.forename: Walter A
authors.initials: WA
authors.lastname: Scott
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D019380:Anti-HIV Agents / Q000494:pharmacology; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D002460:Cell Line; D017931:DNA Primers / Q000378:metabolism; D004279:DNA, Viral / Q000235:genetics*; D003838:Deoxyadenine Nucleotides / Q000494:pharmacology; D054306:Dideoxynucleotides; D011756:Diphosphates / Q000378:metabolism; D024882:Drug Resistance, Viral; D054303:HIV Reverse Transcriptase / Q000235:genetics*; D015497:HIV-1 / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects / Q000502:physiology*; D008214:Lymphocytes / Q000187:drug effects / Q000502:physiology*; D015215:Zidovudine / Q000494:pharmacology
chemical_list: D019380:Anti-HIV Agents; D017931:DNA Primers; D004279:DNA, Viral; D003838:Deoxyadenine Nucleotides; D054306:Dideoxynucleotides; D011756:Diphosphates; C010110:2',3'-dideoxyadenosine 5'-phosphate; D015215:Zidovudine; D000255:Adenosine Triphosphate; D054303:HIV Reverse Transcriptase