High molecular weight deoxyribonucleic acid polymerase of LF hepatoma. Purification and properties.

A high molecular weight DNA polymerase has been purified from the cytosol of a fast growing hepatoma: LF hepatoma. This enzyme sediments at 11.3 S under polymerization reaction conditions (6 mM KCl) and at 8.3 S in higher salt concentrations (200 mM KCl). In either case, no activity is seen in the 3 to 4 S region where low molecular weight DNA polymerase is found. The purified enzyme has a neutral pH optimum and requires a divalent cation, all four deoxyribonucleoside triphosphates and an initiated DNA template for maximal activity. The synthetic template specificity of LF DNA polymerase has been studied. Although this enzyme cannot copy a polyribonucleotide template, the ribostrand of a synthetic hybrid can be used with low efficiency as an initiator for the synthesis of the complementary deoxyribonucleotide strand. The activity of the purified enzyme is strongly inhibited by thiol-blocking agents. The general properties of LF DNA polymerase are similar to those of high molecular weight mammalian DNA polymerases. In our experimental conditions, the error frequency of this tumoral DNA polymerase was no greater than that made by the purified high molecular weight DNA polymerase of regenerating rat liver.

DNA polymerase-alpha from regenerating rat liver. Catalytic properties of the highly purified enzyme.

DNA polymerase-alpha from the cytosol of regenerating rat liver has been highly purified by a procedure which includes affinity chromatography. The purified enzyme sediments at 7.4 S in high ionic strength and at 9--10 S in low ionic strength, i.e. under in vitro polymerization conditions. This enzyme has all the properties of the other mammalian DNA polymerases-alpha: sensitivity to sulfhydryl-blocking agents, to heparin, and to the level of salt in the assay, neutral pH optimum, use of ribonucleotide-initiated DNA templates, and inability to copy the ribostrand of hybrids. After chromatography on denatured DNA-cellulose, the alpha-polymerase is completely devoid of exo- and endonuclease activities. Template competition experiments indicate that the binding of the enzyme to the template can be distinguished from the polymerization itself and that the in vitro synthesis catalyzed by this alpha-polymerase is not distributive in a classical sense. These facts are discussed.

A DNA polymerase from a thermoacidophilic archaebacterium: evolutionary and technological interests.

The archaebacteria constitute a group of prokaryotes with an intermediate phylogenetic position between eukaryotes and eubacteria. The study of their DNA polymerases may provide valuable information about putative evolutionary relationships between prokaryotic and eukaryotic DNA polymerases. As a first step towards this goal, we have purified to near homogeneity a DNA polymerase from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius. This enzyme is a monomeric protein of 100 kDa which can catalyze DNA synthesis using either activated calf thymus DNA or oligonucleotide-primed single-stranded DNA as a template. The activity is optimal at 70 degrees C and the enzyme is thermostable up to 80 degrees C; however, it can still polymerize up to 200 nucleotides at 100 degrees C. These remarkable thermophilic properties and thermostability permit examination of the mechanism of DNA synthesis under conditions of decreased stability of the DNA helix. Furthermore, these properties make S. acidocaldarius DNA polymerase a very efficient enzyme to be used in DNA amplification by the recently developed polymerase chain reaction method (PCR) as well as in the Sanger DNA sequencing technique.

Characterization of the POL3 gene product from Schizosaccharomyces pombe indicates inter-species conservation of the catalytic subunit of DNA polymerase delta.

The Schizosaccharomyces pombe POL3 gene was isolated by sequence homology with a region of the Saccharomyces cerevisiae POL3 gene, the only gene sequenced to date encoding the catalytic subunit of eukaryotic DNA polymerase delta. The fission yeast POL3 gene contains a 52 base-pair (bp) intron and encodes a 3600 bp transcript the 5'-end of which is located 32 bp upstream from the initiation codon. The polypeptides predicted from budding and fission yeast POL3 genes share 52% of conserved amino acid residues and have a 60% identical central region. This structural conservation of the catalytic subunit of DNA polymerases delta is probably related to functional constraints. A portion of the most conserved region was used to raise antibodies against an S. pombe polymerase delta/beta-galactosidase fusion protein expressed in Escherichia coli. The purified antibodies recognized a 123,000 Da protein in S. pombe wild-type cell extracts and inhibited an aphidicolin-sensitive DNA polymerase activity that was distinct from DNA polymerase alpha. The antibodies also detected a 140,000 Da protein in extracts from different proliferating mammalian cells, indicating that the catalytic subunits of DNA polymerase delta are highly conserved between yeast and higher eukaryotes.

DNA polymerase from Sulfolobus acidocaldarius. Replication at high temperature of long stretches of single-stranded DNA.

The activity of a homogeneous DNA polymerase from the thermophilic archaebacterium, Sulfolobus acidocaldarius, on a singly primed, single-stranded recombinant phage M13 DNA has been examined. At the optimal temperature (70 to 75 degrees C) this template is efficiently replicated in ten minutes using a ratio of enzyme molecule to primed-template of 0.8. Analysis of DNA products during the course of polymerization shows that species of quite homogeneous size are observed and that the number of primers extended by the enzyme is constant, whatever the enzyme molecule to primed template ratio is in the range 1/50 to 2, indicating that the 100 x 10(3) Mr DNA polymerase from S. acidocaldarius is randomly recycled on the template molecules. At non-optimal temperature (60 degrees C and 80 degrees C) the distribution of products observed indicated the presence of arrest sequences; some have been shown to be reversible. One of these pausing signals detected at 80 degrees C has been further analysed, and has been found to be DNA sequence-dependent.

Peduncular 'rubral' tremor and dopaminergic denervation: a PET study.

Lesions causing so-called rubral tremors frequently involve the substantia nigra or the nigrostriatal fibers, suggesting dopaminergic denervation as possibly contributory. We examined this hypothesis using PET and [18F]-fluorodopa in six patients with a contralateral tremor following a peduncular lesion. The denervation revealed by PET was even more marked than in severe parkinsonian patients. All patients showed partial to complete improvement with levodopa therapy. PET evaluation of D2-receptors with [76Br]bromolisuride showed no asymmetry of the D2 binding despite the important asymmetry of 18F-fluorodopa uptake. Our results indicate an important involvement of the nigral dopaminergic system in peduncular tremors that appears to be independent of postsynaptic dopamine receptors.

Rat liver DNA polymerase-beta: thermal inactivation of RNA- and DNA-dependent activities.

Purified DNA polymerase-beta from rat liver was exposed to thermal inactivation and the remaining activities were then measured either with a hybrid template such as poly(A).(dT)12-18 (R-activity) or with a DNA template such as poly(dA).(dT)12-18 (D-activity). Time course of inhibition of R- and D-activities were identical. Neither activity was protected when the thermal treatment was performed in the presence of the template or dNTPs.

[Positron-emission tomographic study of the dopaminergic system in a case of secondary unilateral tremor after mesencephalic hematoma]. / Etude du système dopaminergique en tomographie par émission de positons dans un cas de tremblement unilatéral secondaire à un hématome mésencéphalique.

A 30 year-old woman developed a postural and rest tremor of the left hand following a right peduncular post-traumatic hematoma. Two years later, positron emission tomography showed a marked decrease in [18F] fluorodopa uptake contrasting with a normal [76Br] bromolisuride uptake in the right striatum. This suggests that: 1) chronic unilateral dopaminergic striatal denervation may occur without persistent D2 dopaminergic receptor upregulation in humans; and 2) symptomatic mesencephalic tremor may be, at least in part, related to dopaminergic striatal denervation.