Multiple deoxyribonucleic acid polymerases from quiescent wheat embryos. Purification and characterization of three enzymes from the soluble cytoplasm and one from purified mitochondria.
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ABSTRACT:
SUBMITTER: Castroviejo M
PROVIDER: S-EPMC1161140 | biostudies-other | 1979 Jul
REPOSITORIES: biostudies-other
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Project description:In order to ascertain the identity of the DNA-dependent DNA polymerase responsible for the observed DNA synthesis in nuclei isolated from baby-hamster kidney (BHK-21/C13) cells a comparative study was carried out on the effects of some drugs, reported to influence DNA synthesis, on DNA synthesis catalysed by these nuclei and by partially purified DNA polymerase-alpha and -beta. In all cases DNA synthesis by isolated nuclei and polymerase-alpha was inhibited to similar extents by N-ethylmaleimide, p-hydroxymercuribenzoate, novobiocin, heparin and phosphonoacetic acid; polymerase-beta was much less affected by these compounds. Ethidium bromide inhibited all DNA synthesis to similar extents, although at low concentrations (about 2 microgram/ml) synthesis in isolated nuclei was stimulated. The results are discussed in relation to the proposal that DNA polymerase-alpha catalyses the covalent extension of Okazaki fragments that these nuclei carry out in vitro.
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Project description:1. DNA polymerase from nuclear and supernatant fractions of cultured mouse L929 cells was fractionated on columns of Sephadex G-200, Sepharose 4B and of DEAE-cellulose. Several peaks of activity are found on Sephadex chromatography and the distribution of activity between these depends on: (a) the source of the enzyme, i.e. nuclear or supernatant fraction; (b) the mode of extraction of the enzyme from the nucleus; (c) the amount of enzyme applied to the column. 2. The DNA polymerase activity in the lower-molecular-weight peaks (approximate molecular weights are 35000, 70000 and 140000) is firmly bound within the cell nucleus and shows a preference for native DNA as template, whereas the high-molecular-weight peak (peak I, molecular weight 250000 or greater) is found in supernatant fractions and shows greater activity with a denatured DNA template. 3. During periods of DNA synthesis the high-molecular-weight enzyme becomes more firmly bound within the nucleus. 4. Peak I enzymic activity is relatively unstable and is inhibited by thiol-blocking reagents and deoxycholate, but it is stimulated by univalent cations. 5. Very little endonuclease is present in the polymerase preparations, but a very active exonuclease and nucleoside diphosphokinase are present. On Sephadex chromatography, however, it was shown that the immediate precursors for DNA synthesis, at least by peak I enzyme, are the deoxyribonucleoside triphosphates. 6. Attempts to decrease the molecular weight of the peak I enzyme while still retaining activity failed.
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Project description:DNA polymerase from BHK-21/C13 cells were separated into two species, DNA polymerase I corresponding to the heterogeneous enzyme with sedimentation coefficient of 6-8S, and DNA polymerase II, corresponding to the enzyme with sedimentation coefficient of 3.3S. DNA polymerase I was purified 114-fold and DNA polymerase II 154-fold by a simple extraction procedure followed by column chromatography on phosphocellulose and gel filtration through Sephadex G-100. The purified enzymes differed markedly in respect of pH optimum, stimulation and inhibition by K+, Km for the deoxyribonucleoside 5'-triphosphates, stability to heating at 45 degrees C, and inhibition by N-ethylmaleimide. The preferred primer-template for both enzymes was "activated" DNA (DNA submitted to limited degradation by pancreatic deoxyribonuclease); native or thermally denatured DNA templates were relatively very poorly copied. When certain synthetic templates were tested, substantial differences were revealed between the two enzymes. Poly[d(A-T)] was poorly used by polymerase I but was superior to "activated" DNA for polymerase II. Poly[d(A)]-oligo[d(pT)10] was used efficiently by polymerase I but not by polymerase II. Poly(A)-oligo[d(pT)10] was not an effective primer-template although polymerase I could use it to a limited extent when Mn2+ replaced Mg2+ in the polymerase reaction and when the temperature of incubation was lowered from 37 degrees to 30 degrees C. When only one or two or three triphosphates were supplied in the reaction mixture, the activity of polymerase I was more severly diminished than that of polymerase II.
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Project description:Causal links exist between smoking cigarettes and cancer development. Some genotoxic agents in cigarette smoke are capable of alkylating nucleobases in DNA, and higher levels of ethylated DNA lesions were observed in smokers than in nonsmokers. In this study, we examined comprehensively how the regioisomeric O(2)-, N3-, and O(4)-ethylthymidine (O(2)-, N3-, and O(4)-EtdT, respectively) perturb DNA replication mediated by purified human DNA polymerases (hPols) ?, ?, and ?, yeast DNA polymerase ? (yPol ?), and the exonuclease-free Klenow fragment (Kf(-)) of Escherichia coli DNA polymerase I. Our results showed that hPol ? and Kf(-) could bypass all three lesions and generate full-length replication products, whereas hPol ? stalled after inserting a single nucleotide opposite the lesions. Bypass conducted by hPol ? and yPol ? differed markedly among the three lesions. Consistent with its known ability to efficiently bypass the minor groove N(2)-substituted 2'-deoxyguanosine lesions, hPol ? was able to bypass O(2)-EtdT, though it experienced great difficulty in bypassing N3-EtdT and O(4)-EtdT. yPol ? was only modestly blocked by O(4)-EtdT, but the polymerase was strongly hindered by O(2)-EtdT and N3-EtdT. LC-MS/MS analysis of the replication products revealed that DNA synthesis opposite O(4)-EtdT was highly error-prone, with dGMP being preferentially inserted, while the presence of O(2)-EtdT and N3-EtdT in template DNA directed substantial frequencies of misincorporation of dGMP and, for hPol ? and Kf(-), dTMP. Thus, our results suggested that O(2)-EtdT and N3-EtdT may also contribute to the AT ? TA and AT ? GC mutations observed in cells and tissues of animals exposed to ethylating agents.
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Project description:Two DNA polymerases of high molecular weight, pol A (mol.wt. 190 000) and pol B (mol.wt. 240 ooo), have been purified 6300-fold and 1600-fold respectively from an extramitochondrial supernatant of a bleached strain of Euglena gracilis. They have very similar requirements when assayed with an 'activated'-DNA primer-template [the optimum conditions of pH and ionic (K+ and Mn2+) composition being 7.2, 25 mM and 0.2 mM respectively]. 0.2 mM-Mn2+ was about 1.5-2-fold as effective as 2 mM-Mg2+, owing to substrate activation by deoxyribonucleoside 5'-triphosphates in the presence of Mn2+. Km values for the triphosphates in the absence of activation were about 10(-6)M with Mn2+ and 8 X 10(-6) M with Mg2+ for both enzymes. They were inhibited to the same extent by N-ethylmaleimide, novobiocin and o-phenanthroline, but differed in their chromatographic behaviour on DEAE-cellulose and in their electrophoretic mobilities on polyacrylamide gel. No evidence was found for the existence in these cells of a DNA polymerase of low molecular weight, but there were indications that a third enzyme of high molecular weight might exist.
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Project description:Four DNA polymerases from the marine diatom Cylindrotheca fusiformis, polymerases A, B, C and D, were further differentiated by their subcellular localization, presence of deoxyribonuclease activity, apparent heterogeneity and molecular weights. Polymerases A, B and D occur in significant amounts in the soluble fraction, suggesting that they were originally localized in the nuclei, whereas polymerase C predominates in the chloroplasts. A mitochondrial DNA polymerase was also isolated and characterized by ion-exchange chromatography. Polymerase D has an associated nuclease activity which prefers denatured DNA and Mg2+, and has a pH optimum higher than that for polymerase activity. Co-elution from a DEAE-Sephadex column and co-sedimentation in glycerol density gradients of deoxyribonuclease and polymerase D activity suggest a molecular association. Polymerases A, B and C are devoid of nuclease activity. Glycerol-gradient-sedimentation analysis showed that all DNA polymerase fractions are heterogeneous at low ionic strengths, with the appearance of a single homogeneous activity of 0.5M-KCl. Estimated molecular weights of 100000, 82000 and 120000 for polymerases A, B and C respectively were obtained from sedimentation analysis and gel filtration. Polymerase D was estimated to have a molecular weight of about 100000 as determined by sedimentation analysis alone.
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Project description:Coronaviruses and arteriviruses are distantly related human and animal pathogens that belong to the order Nidovirales. Nidoviruses are characterized by their polycistronic plus-stranded RNA genome, the production of subgenomic mRNAs and the conservation of a specific array of replicase domains, including key RNA-synthesizing enzymes. Coronaviruses (26-34 kilobases) have the largest known RNA genomes and their replication presumably requires a processive RNA-dependent RNA polymerase (RdRp) and enzymatic functions that suppress the consequences of the typically high error rate of viral RdRps. The arteriviruses have significantly smaller genomes and form an intriguing package with the coronaviruses to analyse viral RdRp evolution and function. The RdRp domain of nidoviruses resides in a cleavage product of the replicase polyprotein named non-structural protein (nsp) 12 in coronaviruses and nsp9 in arteriviruses. In all nidoviruses, the C-terminal RdRp domain is linked to a conserved N-terminal domain, which has been coined NiRAN (nidovirus RdRp-associated nucleotidyl transferase). Although no structural information is available, the functional characterization of the nidovirus RdRp and the larger enzyme complex of which it is part, has progressed significantly over the past decade. In coronaviruses several smaller, non-enzymatic nsps were characterized that direct RdRp function, while a 3'-to-5' exoribonuclease activity in nsp14 was implicated in fidelity. In arteriviruses, the nsp1 subunit was found to maintain the balance between genome replication and subgenomic mRNA production. Understanding RdRp behaviour and interactions during RNA synthesis and subsequent processing will be key to rationalising the evolutionary success of nidoviruses and the development of antiviral strategies.
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Project description:1. Both the acid-soluble fraction and the nucleic acid fraction of wheat embryos were extensively labelled after incubation for 6hr. in the presence of [8-(14)C]adenine. Subsequent incubation in the absence of labelled adenine resulted in no loss of radioactivity to the medium during a 48hr. period. Radioautography indicated that during this period there was a continuous increase in the radioactivity present in the acid-insoluble fractions of the root and leaf tissues relative to that present in the coleorhiza and coleoptile. 2. During incubation at 25 degrees there was a 26-fold increase in the activity of 3'-nucleotidase between 4hr. and 24hr.; the activities of enzymes hydrolysing AMP and IMP increased to a smaller extent. The activities of adenine phosphoribosyltransferase and hypoxanthine phosphoribosyltransferase increased three- to five-fold during incubation at 25 degrees for 24hr. 3. Adenosine kinase, inosine phosphorylase and 5-phosphoribosyl pyrophosphate synthetase activities were high in extracts from dry embryos and did not increase during 48hr. at 25 degrees . 4. The increase in 3'-nucleotidase activity was prevented by cycloheximide, cryptopleurine or incubation at 4 degrees , but not by actinomycin D; these treatments did not depress the activity of the other enzymes measured. 5. The results are discussed in relation to RNA translocation within the wheat embryo during germination.
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Project description:Successful mammalian cloning using somatic cell nuclear transfer (SCNT) into unfertilized, metaphase II (MII)-arrested oocytes attests to the cytoplasmic presence of reprogramming factors capable of inducing totipotency in somatic cell nuclei. However, these poorly defined maternal factors presumably decline sharply after fertilization, as the cytoplasm of pronuclear-stage zygotes is reportedly inactive. Recent evidence suggests that zygotic cytoplasm, if maintained at metaphase, can also support derivation of embryonic stem (ES) cells after SCNT, albeit at low efficiency. This led to the conclusion that critical oocyte reprogramming factors present in the metaphase but not in the interphase cytoplasm are 'trapped' inside the nucleus during interphase and effectively removed during enucleation. Here we investigated the presence of reprogramming activity in the cytoplasm of interphase two-cell mouse embryos (I2C). First, the presence of candidate reprogramming factors was documented in both intact and enucleated metaphase and interphase zygotes and two-cell embryos. Consequently, enucleation did not provide a likely explanation for the inability of interphase cytoplasm to induce reprogramming. Second, when we carefully synchronized the cell cycle stage between the transplanted nucleus (ES cell, fetal fibroblast or terminally differentiated cumulus cell) and the recipient I2C cytoplasm, the reconstructed SCNT embryos developed into blastocysts and ES cells capable of contributing to traditional germline and tetraploid chimaeras. Last, direct transfer of cloned embryos, reconstructed with ES cell nuclei, into recipients resulted in live offspring. Thus, the cytoplasm of I2C supports efficient reprogramming, with cell cycle synchronization between the donor nucleus and recipient cytoplasm as the most critical parameter determining success. The ability to use interphase cytoplasm in SCNT could aid efforts to generate autologous human ES cells for regenerative applications, as donated or discarded embryos are more accessible than unfertilized MII oocytes.
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Project description:A DNA polymerase-endogenous template complex was isolated from nuclear heads of bull spermatozoa. The buoyant density of the complex was 1.15 g/cm 3. The sedimentation coefficient of the nuclear DNA polymerase isolated from the complex was higher at low ionic strength, but approached 3.4S when centrifuged in a medium containing 2M-KCl. Activated exogenous DNA increased polymerase activity. Only very low activities were detected with synthetic templates such as poly(A).(dT)12-18 and poly(dT).poly(A). The nuclear reaction was stimulated by 150mM-KCl and was slightly inhibited by N-ethylmaleimide; it was resistant to actinomycin D, netropsin and ethidium bromide. Another DNA polymerase, highly sensitive to ethidium bromide, was extracted from the mitochondira-rich middle-piece fraction. Its sedimentation coefficient was close to 9S, but fell to approx. 4S in high-ionic-strength medium.
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