The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform

Shinya Shibutani - One of the best experts on this subject based on the ideXlab platform.

Thomas A. Kunkel - One of the best experts on this subject based on the ideXlab platform.

  • The base substitution fidelity of HIV-1 reverse transcriptase on DNA and RNA templates probed with 8-oxo-Deoxyguanosine Triphosphate
    Mutation research, 1999
    Co-Authors: Katarzyna Bebenek, Jayne C. Boyer, Thomas A. Kunkel
    Abstract:

    Abstract We have used 8-O-dGTP, a mutagenic nucleotide generated by oxidative metabolism, to probe the misincorporation potential of HIV-1 reverse transcriptase (RT) during DNA synthesis templated by the same nucleotide sequence as either RNA or DNA. With either template, 8-O-dGMP was misincorporated opposite template A, yielding characteristic A→C transversions. The error rate with DNA was similar to that with RNA, suggesting that base misincorporation by the RT during first-strand and second-strand replication may contribute equally to the HIV-1 base substitution mutation rate. The rate of 8-O-dGMP misincorporation differed by more than 10-fold among the 20 adenines in the M13mp2 template where A→C transversions can be detected. The transversion distribution was similar with the two templates, indicating that the effects of flanking nucleotides on misincorporation rates were similar. This is consistent with structural and biochemical data suggesting that HIV-1 RT binds RNA·DNA and DNA·DNA template–primers in the same orientation. The similarities in error rates and distribution further indicate that, despite differences in the structures of free RNA·DNA and DNA·DNA duplexes (e.g., minor groove dimensions), the polymerase active site that assembles upon substrate binding establishes a similar degree of nucleotide selectivity with both types of template–primers. Comparison of the RT error distribution to that observed with two Pol I family DNA polymerases and a Pol α family polymerase revealed common hot and cold spots for misincorporation. This suggests that the local nucleotide sequence influences the nucleotide selectivity of four polymerases in a similar manner, despite their differences in structure, biochemical properties, and functions.

  • Accelerated publication The base substitution fidelity of HIV-1 reverse transcriptase on DNA and RNA templates probed with 8-oxo-Deoxyguanosine Triphosphate
    1999
    Co-Authors: Katarzyna Bebenek, Jayne C. Boyer, Thomas A. Kunkel
    Abstract:

    We have used 8-O-dGTP, a mutagenic nucleotide generated by oxidative metabolism, to probe the misincorporation . potential of HIV-1 reverse transcriptase RT during DNA synthesis templated by the same nucleotide sequence as either RNA or DNA. With either template, 8-O-dGMP was misincorporated opposite template A, yielding characteristic A" C transversions. The error rate with DNA was similar to that with RNA, suggesting that base misincorporation by the RT during first-strand and second-strand replication may contribute equally to the HIV-1 base substitution mutation rate. The rate of 8-O-dGMP misincorporation differed by more than 10-fold among the 20 adenines in the M13mp2 template where A" C transversions can be detected. The transversion distribution was similar with the two templates, indicating that the effects of flanking nucleotides on misincorporation rates were similar. This is consistent with structural and biochemical data suggesting that HIV-1 RT binds RNAP DNA and DNAP DNA template-primers in the same orientation. The similarities in error rates and distribution further indicate that, despite differences in the structures of free RNA P DNA and DNAP DNA . duplexes e.g., minor groove dimensions , the polymerase active site that assembles upon substrate binding establishes a similar degree of nucleotide selectivity with both types of template-primers. Comparison of the RT error distribution to that observed with two Pol I family DNA polymerases and a Pol a family polymerase revealed common hot and cold spots for misincorporation. This suggests that the local nucleotide sequence influences the nucleotide selectivity of four polymerases in a similar manner, despite their differences in structure, biochemical properties, and functions. q 1999 Elsevier Science B.V. All rights reserved.

Tomonari Matsuda - One of the best experts on this subject based on the ideXlab platform.

David Back - One of the best experts on this subject based on the ideXlab platform.

  • Mycophenolate mofetil inhibits T-cell proliferation in kidney transplant recipients without lowering intracellular dGTP and GTP.
    Transplant international : official journal of the European Society for Organ Transplantation, 2008
    Co-Authors: Sanjay U. C. Sankatsing, David Back, Jan M. Prins, Sila L. Yong, Jeroen Roelofsen, André B.p. Van Kuilenburg, Steve Kewn, Frederike J. Bemelman, Ineke J. M. Ten Berge
    Abstract:

    Summary To study if mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), indeed inhibits T-cell proliferation in kidney transplant recipients by lowering intracellular Deoxyguanosine Triphosphate (dGTP) and guanosine Triphosphate (GTP) levels. Blood was drawn from 11 kidney transplant recipients. Ex vivo T-cell proliferation was measured by stimulation with phytohemagglutin (PHA) and anti-CD3 monoclonal antibody (mAb). Plasma MPA levels and intracellular dGTP and GTP in peripheral blood mononuclear cells were measured. MMF induces a significant decrease in T-lymphocyte proliferation at all time points (i.e. 24 h, 10 days and 8 weeks) after stimulation with both PHA (P = 0.001, 0.002 and 0.013 respectively) and anti-CD3 mAb (P = 0.004, 0.004 and 0.005 respectively). There was no significant change in intracellular dGTP (P = 0.31, 0.16 and 0.35) or GTP levels (P = 0.99, 0.32 and 0.49) between baseline and day 1, day 10 or week 8. All MPA levels were above the minimal required concentration for the inhibition of lymphocyte proliferation. MMF inhibits T-lymphocyte proliferation in kidney transplant recipients without lowering intracellular dGTP or GTP levels. This suggests another mechanism underlying its immunosuppressive capacity.

  • Effect of Mycophenolate Mofetil on the Pharmacokinetics of Antiretroviral Drugs and on Intracellular Nucleoside Triphosphate Pools
    Clinical pharmacokinetics, 2004
    Co-Authors: Sanjay U. C. Sankatsing, Stephen Kewn, David Back, Patrick G. Hoggard, Alwin D. R. Huitema, Rolf W. Sparidans, Kristel M. L. Crommentuyn, Joep M. A. Lange, Jos H. Beijnen, Jan M. Prins
    Abstract:

    Objective To study the effect of mycophenolate mofetil therapy on the pharmacokinetic parameters of a number of antiretroviral drugs, on intracellular pools of deoxycytidine Triphosphate (dCTP) and Deoxyguanosine Triphosphate (dGTP), and on intracellular concentrations of the Triphosphate of lamivudine (3TCTP).

  • The addition of mycophenolate mofetil to antiretroviral therapy including abacavir is associated with depletion of intracellular Deoxyguanosine Triphosphate and a decrease in plasma HIV-1 RNA
    Journal of acquired immune deficiency syndromes (1999), 2002
    Co-Authors: David M. Margolis, Stephen Kewn, Jason J. Coull, Loyda Ylisastigui, Diana Turner, Holly Wise, Mohammed M. Hossain, E. Randall Lanier, Leslie M. Shaw, David Back
    Abstract:

    Mycophenolic acid (MPA) enhances the in vitro activity of abacavir (ABC) and other nucleoside analog reverse transcriptase inhibitors (NRTIs) against sensitive and NRTI-resistant HIV-1. This may occur via depletion of intracellular Deoxyguanosine Triphosphate (dGTP). Mycophenolate mofetil (MMF) 500 mg twice daily was added as a single agent to the antiretroviral regimens of five patients failing maximal available therapy. Therapy included ABC, and in most cases didanosine (DDI) and tenofovir (TDF). At entry, mean plasma HIV-1 RNA (VL) was 5.02 log copies/mL (median 4.78, range 4.71-5.63) and mean CD4 count was 106/microL (median 117, range 11-174). MMF was well tolerated. CD4 cell counts did not change significantly from baseline for up to 60 weeks of follow-up. Three of five subjects had VL declines of >0.5 log copies/mL immediately after adding MMF; a fourth subject had a sustained decline of >0.5 log copies/mL after week 8. Declines of >0.5 log copies/mL were lost in two patients at 6 and 8 weeks, and persisted in two patients at 36 and 60 weeks of follow-up, respectively. An increase in the ratio of carbovir Triphosphate (CBV-TP), the active antiviral metabolite of ABC, to dGTP was documented in 3 of 4 subjects in temporal association with decreased VL. Trough plasma MPA levels ranged from 0.26-1.67 microg/mL; peak levels 90 minutes after dosing from 1.20-7.77 microg/mL. AUC of MPA appeared little changed when measured over 28 weeks of therapy. Declines in VL were observed in association with measurable changes in the CBV-TP/dGTP ratio in some patients, whereas MPA AUC was below the 30-60 microg*hr/mL range targeted in organ transplantation. The possibility that MMF may enhance the effect of selected NRTIs and be tolerated in late stage HIV disease deserves careful randomized study.

Michael Chang - One of the best experts on this subject based on the ideXlab platform.

  • telomere length homeostasis responds to changes in intracellular dntp pools
    Genetics, 2013
    Co-Authors: Amitabha Gupta, Sushma Sharma, Patrick Reichenbach, Lisette Marjavaara, Anna Karin Nilsson, Joachim Lingner, Andrei Chabes, Rodney Rothstein, Michael Chang
    Abstract:

    Telomeres, the ends of linear eukaryotic chromosomes, shorten due to incomplete DNA replication and nucleolytic degradation. Cells counteract this shortening by employing a specialized reverse transcriptase called telomerase, which uses deoxyribonucleoside Triphosphates (dNTPs) to extend telomeres. Intracellular dNTP levels are tightly regulated, and perturbation of these levels is known to affect DNA synthesis. We examined whether altering the levels of the dNTP pools or changing the relative ratios of the four dNTPs in Saccharomyces cerevisiae would affect the length of the telomeres. Lowering dNTP levels leads to a modest shortening of telomeres, while increasing dNTP pools has no significant effect on telomere length. Strikingly, altering the ratio of the four dNTPs dramatically affects telomere length homeostasis, both positively and negatively. Specifically, we find that intracellular Deoxyguanosine Triphosphate (dGTP) levels positively correlate with both telomere length and telomerase nucleotide addition processivity in vivo. Our findings are consistent with in vitro data showing dGTP-dependent stimulation of telomerase activity in multiple organisms and suggest that telomerase activity is modulated in vivo by dGTP levels.