Effect of fixation time on measurement of 2'-deoxyribonucleoside 5'-triphosphate pools in the rat embyro.
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ABSTRACT:
SUBMITTER: Ritter EJ
PROVIDER: S-EPMC1186684 | biostudies-other | 1979 Jun
REPOSITORIES: biostudies-other
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Project description:The size of the deoxyribonucleoside triphosphate pools of vitamin B-12-deficient cells of Euglena gracilis, and of vitamin B-12-deficient cells repleted with the vitamin, were measured. We found that the pools were very small, if they exist at all, in deficient cells but expand rapidly with the addition of the vitamin. The sizes of the pools decrease when DNA synthesis is completed, and are very small when the cells begin to divide.
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Project description:The deoxyribonucleoside triphosphate pools are undetectable in vitamin B-12-deficient cells of Euglena gracillis, but appear rapidly after the replenishment with the vitamin. They reach a maximum size that is about 6 times that of normal exponentially growing cells, but decrease to almost zero as the cells divide. The pools expand again during the post-replenishment shortened cell cycle. However, the expansion takes place during rather than before the resumption of DNA synthesis. The maximum sizes reached are still larger than in normal cells. By using the protein-synthesis inhibitor cycloheximide and determining the pool size, we found that vitamin-deficient cells apparently accumulate a large amount of ribonucleoside triphosphate reductase apoenzyme, which lacks the vitamin B12 coenzyme. We showed that the production of the deoxyribonucleoside triphosphates is not closely coupled to DNA synthesis under our experimental conditions, and that the concentration of the deoxyribonucleoside triphosphate pools per unit of DNA synthesized is almost constant for all stages of growth examined.
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Project description:EF1143 from Enterococcus faecalis, a life-threatening pathogen that is resistant to common antibiotics, is a homo-tetrameric deoxyribonucleoside triphosphate (dNTP) triphosphohydrolase (dNTPase), converting dNTPs into the deoxyribonucleosides and triphosphate. The dNTPase activity of EF1143 is regulated by canonical dNTPs, which simultaneously act as substrates and activity modulators. Previous crystal structures of apo-EF1143 and the protein bound to both dGTP and dATP suggested allosteric regulation of its enzymatic activity by dGTP binding at four identical allosteric sites. However, whether and how other canonical dNTPs regulate the enzyme activity was not defined. Here, we present the crystal structure of EF1143 in complex with dGTP and dTTP. The new structure reveals that the tetrameric EF1143 contains four additional secondary allosteric sites adjacent to the previously identified dGTP-binding primary regulatory sites. Structural and enzyme kinetic studies indicate that dGTP binding to the first allosteric site, with nanomolar affinity, is a prerequisite for substrate docking and hydrolysis. Then, the presence of a particular dNTP in the second site either enhances or inhibits the dNTPase activity of EF1143. Our results provide the first mechanistic insight into dNTP-mediated regulation of dNTPase activity.
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Project description:The deoxyribonucleoside triphosphate (dNTP) pools that support the replication of mitochondrial DNA are physically separated from the rest of the cell by the double membrane of the mitochondria. Perturbed homeostasis of mitochondrial dNTP pools is associated with a set of severe diseases collectively termed mitochondrial DNA depletion syndromes. The degree of interaction of the mitochondrial dNTP pools with the corresponding dNTP pools in the cytoplasm is currently not clear. We reviewed the literature on previously reported simultaneous measurements of mitochondrial and cytoplasmic deoxyribonucleoside triphosphate pools to investigate and quantify the extent of the influence of the cytoplasmic nucleotide metabolism on mitochondrial dNTP pools. We converted the reported measurements to concentrations creating a catalog of paired mitochondrial and cytoplasmic dNTP concentration measurements. Over experiments from multiple laboratories, dNTP concentrations in the mitochondria are highly correlated with dNTP concentrations in the cytoplasm in normal cells in culture (Pearson R = 0.79, p = 3 × 10(-7)) but not in transformed cells. For dTTP and dATP there was a strong linear relationship between the cytoplasmic and mitochondrial concentrations in normal cells. From this linear model we hypothesize that the salvage pathway within the mitochondrion is only capable of forming a concentration of approximately 2 ?M of dTTP and dATP, and that higher concentrations require transport of deoxyribonucleotides from the cytoplasm.
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Project description:Newly identified anti-HIV host factor, SAMHD1, restricts replication of lentiviruses such as HIV-1, HIV-2, and simian immunodeficiency virus in macrophages by enzymatically hydrolyzing and depleting cellular dNTPs, which are the substrates of viral DNA polymerases. HIV-2 and some simian immunodeficiency viruses express viral protein X (VPX), which counteracts SAMHD1 and elevates cellular dNTPs, enhancing viral replication in macrophages. Because nucleoside reverse transcriptase inhibitors (NRTIs), the most commonly used anti-HIV drugs, compete against cellular dNTPs for incorporation into proviral DNA, we tested whether SAMHD1 directly affects the efficacy of NRTIs in inhibiting HIV-1. We found that reduction of SAMHD1 levels with the use of virus-like particles expressing Vpx- and SAMHD1-specific shRNA subsequently elevates cellular dNTPs and significantly decreases HIV-1 sensitivity to various NRTIs in macrophages. However, virus-like particles +Vpx treatment of activated CD4(+) T cells only minimally reduced NRTI efficacy. Furthermore, with the use of HPLC, we could not detect SAMHD1-mediated hydrolysis of NRTI-triphosphates, verifying that the reduced sensitivity of HIV-1 to NRTIs upon SAMHD1 degradation is most likely caused by the elevation in cellular dNTPs.
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