DNA polymerase I, Klenow fragment of Escherichia coli: hydrolysis and pyrophosphorolysis of DNA containing phosphothioate groups

Reaction of DNA synthesis catalyzed by DNA polymerase I KF in the presence of 2'-deoxynucleoside 5'-alpha-thiotriphosphates (dNTP alpha S) was investigated. DNA with thiophosphate groups (DNA[P=S]) obtained by such a way was studied in reactions of hydrolysis and pyrophosphorolysis catalyzed by DNA polymerase I KF. It is shown that the rate of DNA elongation is decreased both on the step of incorporation of dNMP alpha S residues and on the step of incorporation of the next dNMP residue. The rate of pyrophosphorolysis of 3'-terminal dNMP alpha S was demonstrated to be one order of magnitude less in comparison with the corresponding reaction with the natural dNMP residue. Contrary, the rate of 3'----5'-exonuclease hydrolysis of both DNA[P=S] and DNA of the same structure revealed no distinguishable differences.     

Role of fatty acid elongases in determination of de novo synthesized monounsaturated fatty acid species

Enhanced production of monounsaturated fatty acids (FA) derived from carbohydrate-enriched diets has been implicated in the development of obesity and insulin resistance. The FA elongases Elovl-5 and Elovl-6 are regulated by nutrient and hormone status, and have been shown using intact yeast and mammalian microsome fractions to be involved in the synthesis of monounsaturated FAs (MUFA). Herein, targeted knockdown and overexpression of Elovl-5 or Elovl-6 was used to determine their roles in de novo synthesis of specific MUFA species in mammalian cells. Treatment of rat insulinoma (INS)-1 cells with elevated glucose increased de novo FA synthesis and the ratio of MUFAs to saturated FAs. Elovl-5 knockdown decreased elongation of 16:1,n-7. Elovl-5 overexpression increased synthesis of 18:1,n-7; however, this increase was dependent on stearoyl-CoA desaturase–driven 16:1,n-7 availability. Knockdown of Elovl-6 decreased elongation of 16:0 and 16:1,n-7, resulting in accumulation of 16:1,n-7. Elovl-6 overexpression preferentially drove synthesis of 16:0 elongation products 18:0 and 18:1,n-9 but not 18:1,n-7. These findings demonstrate that coordinated induction of FA elongase and desaturase activity is required for balanced synthesis of specific n-7 versus n-9 MUFA species. Given the relative abundance of 16:0 to 16:1,n-7 and the specificity of Elovl-6 for 16:0, Elovl-6 is a major elongase for 18:1,n-9 production.     

Adenosine 3′:5′-cyclic monophosphate and catabolite repression in Escherichia coli

1. Both permanent and transient catabolite repression of beta-galactosidase synthesis in Escherichia coli are abolished by 5mm-3':5'-cyclic-AMP when elicited by glucose, but not when caused by a mixture of glucose, glucose 6-phosphate, gluconate and casein hydrolysate (casamino acids). 2. Glucose uptake is slightly increased by 3':5'-cyclic-AMP. 3. No significant effects of the nucleotide were found on the synthesis of protein and RNA, either in exponential growth on one substrate, or during a growth shift from glycerol to glycerol plus glucose. 4. Marked changes in the soluble-protein profiles of cells growing in glycerol and glucose were caused by the presence of 3':5'-cyclic-AMP. 5. Measurements of (14)CO(2) release from specifically-labelled glucose showed that 3':5'-cyclic-AMP greatly stimulated glycolytic activity while having a minor depressing effect on the metabolic flow through the pentose phosphate cycle. 6. The concentrations of several metabolic intermediates, particularly fructose 1,6-diphosphate, were greatly affected by the presence of 3':5'-cyclic-AMP. 7. Several metabolites partially relieved glucose repression of beta-galactosidase synthesis in EDTA-treated cells; three out of five of these metabolites reversed the effect more effectively than did 3':5'-cyclic-AMP. 8. The evidence for and against a direct role for 3':5'-cyclic-AMP is discussed. It is concluded that the evidence for indirect action is at least as strong as that for direct action.     

Analogs of (2'-5')oligo(A). Endonuclease activation and inhibition of protein synthesis in intact cells

Synthetic analogs of (2'-5')oligo(A) were assayed for endonuclease activation in cell extracts and for inhibition of protein synthesis in intact cells. The analogs are triadenylates: (i) methylated in the terminal 3'-OH; (ii) methylated at all three 3'-OH groups; (iii) with different numbers of phosphate groups at the 5' terminus or with a methylene group between the beta- and gamma-phosphate. Only 5'-phosphorylated monomethylated analogs activate an endonuclease in cell extracts and are powerful inhibitors of protein synthesis in intact cells. The analogs with only one 5'-terminal phosphate may require addition of another phosphate for activity since the kinase inhibitor 2-aminopurine prevents endonuclease activation by this compound but not by the di- and triphosphate-terminated triadenylates. These results suggest that two terminal phosphates and one or two free 3'-OH are required for endonuclease activation and inhibition of protein synthesis. The monomethylated analogs are more active than (2'-5')pppA3 because of their resistance to degradation by cellular enzymes. Accordingly, the monomethylated analogs cause a prolonged inhibition of protein synthesis in human fibroblasts treated with nanomolar concentrations of these compounds.     

Cleavage and synthesis of sialic acids with aldolase. NMR studies of stereochemistry, kinetics, and mechanisms

1H-NMR spectroscopy was used to study cleavage and synthesis of N-acetyl- and N-glycoloyl-D-neuraminic acid by Clostridium perfringens aldolase. Whereas the alpha-anomers of Neu5Ac and Neu5Gc serve as substrate in the cleavage reaction, alpha-ManNAc and alpha-ManNGc are its primary products. The same alpha-anomers are needed by the aldolase for the synthesis of Neu5Ac and Neu5Gc. During the enzyme reaction in D2O both H-atoms at C-3 of Neu5Ac are exchanged by deuterium, H-3e reacting faster than H-3a. Rate constants and concentrations at equilibrium of reactants are temperature- and pH-dependent: The amount of Neu5Ac in equilibrium increases with decreasing temperature and increasing pH-value. Based on these results a mechanism of aldolase action is discussed.     

Effect of cerebral ganglia and dorsal bodies on DNA synthesis induced by heat in the ovotestis of hibernating Helix aspersa ]

Brain extirpation of snails at the start of their natural hibernation increased the synthesis of DNA in spermatogonia when the animals were transferred from 5 to 25 degrees C for a 4-week period. This effect did not occur if animals were maintained at 5 degrees C. The reimplantation of brain (cerebral ganglia: CG + associated dorsal bodies: DB) in brain-ablated snails failed to correct the effects of brain extirpation. The implantation of either DB or CG in cerebrotomized hosts showed that, compared to shams, DB restored the level of DNA synthesis and spermatogonial proliferations whereas CG stimulated it. The CG and associated DB were therefore found to exert antagonistic effects which are responsible for the control of spermatogonial DNA synthesis in hibernating Helix aspersa.     

Aging of human fibroblasts in vitro. Correlations between DNA synthetic ability and cell size.

In tobacco cell suspensions, protein synthesis and mitotic activity were inhibited by amino acid analogues: p-fluorophenylalanine (pFPA) or 5-methyltryptophan (5MT). After inhibition by pFPA, when the mitotic activity recovered in the presence of phenylalanine and casein hydrolysate, the time table of the mitotic phases was permanently altered. The inhibiting effects of 5MT were effectively reversed by tryptophan addition to the medium. Therefore 5MT was selected for reversible protein synthesis inhibition in partially synchronized cell suspensions. When cytokinin was added in a culture where protein synthesis was inhibited by 5MT, no mitosis was observed after the cells were transferred to a hormone-free medium and protein synthesis restored by tryptophan. Cytokinin must again be added in order to restore mitosis. Thus, the hormone effectiveness of cytokinins required that protein synthesis remained undisturbed. The effect of the protein synthesis inhibition by 5MT upon the metabolism of N⁶-benzyladenine was investigated: the intracellular concentration of this cytokinin was not altered, whereas the metabolic pool of its derivatives was quantitatively reduced.     

Hematopoiesis-stimulating and anti-tumor effects of repeated administration of diclofenac in mice with transplanted fibrosarcoma cells

Positive effects of repeated administration of diclofenac, an inhibitor of prostaglandin synthesis, in terms of prevention of tumor development and stimulation of hematopoiesis have been observed in C3H mice transplanted subcutaneously with G:5:113 fibrosarcoma cells. Fourteen-day treatment with diclofenac (3.75 microg/kg/day) started from day 5 after tumor cell transplantation. Measurements of tumors and hematological examinations were performed on day 30. The results strongly suggest the possibility that inhibitors of prostaglandin synthesis (non-steroidal anti-inflammatory drugs) may be used in oncological practice where the observed effects are highly desirable.     

Molecular basis for differential elongation of omega-3 docosapentaenoic acid by the rat Elovl5 and Elovl2

Functional characterization of the rat elongases, Elovl5 and Elovl2, has identified that Elovl2 is crucial for omega-3 docosahexaenoic acid (DHA) (22:6n-3) synthesis. While the substrate specificities of the rat elongases had some overlap, only Elovl2 can convert the C₂₂ omega-3 PUFA docosapentaenoic acid (DPA) (22:5n-3) to 24:5n-3, which is the penultimate precursor of DHA. In order to better understand the potential for these elongases to be involved in DHA synthesis, we have examined the molecular reasons for the differences between Elovl5 and Elovl2 in their ability to elongate DPA to 24:5n-3. We identified a region of heterogeneity between Elovl5 and Elovl2 spanning transmembrane domains 6 and 7. Using a yeast expression system, we examined a series of Elovl2/Elovl5 chimeras and point mutations to identify Elovl2 residues within this region which are responsible for DPA substrate specificity. The results indicate that the cysteine at position 217 in Elovl2 and a tryptophan at the equivalent position in Elovl5 explain their differing abilities to elongate DPA to 24:5n-3. Further studies confirmed that Elovl2 C217 is a critical residue for elongation of DPA at the level observed in the native protein. Understanding the ability of elongases to synthesize 24:5n-3 may provide a basis for using sequence data to predict their ability to ultimately support DHA synthesis.     

A convenient solid phase approach to obtain lipophilic 5′-phosphoramidate derivatives of DNA and RNA oligonucleotides

This paper explores the potential of a modified phosphotriester approach to the synthesis of 5′-phosphoramidate derivatives of DNA and RNA oligonucleotides. The modification of 5′-deprotected support-bound oligonucleotides is done in two steps: i) conversion of the 5′-OH group of an oligonucleotide into an activated phosphodiester, and ii) treatment of the activated phosphodiester with an aminocompound. The approach is efficient and compatible with conventional solid phase oligonucleotide synthesis. It can be used for the conjugation of therapeutically relevant oligonucleotides with functional moieties or carrier constructions, which are to be removed after endocytosis.     

Synthesis of N-unsubstituted, mono- and disubstituted carbohydrate-1-O-carbamates and their behaviour in glycoside syntheses

The syntheses of 44 1-carbamates from six different 1-O-unprotected carbohydrate derivatives (compounds 1-6), representing typical protecting pattern in glycoside synthesis, are described. The carbamate function is N-unsubstituted (compounds 1b-6b), mono- (compounds a: N-trichloroacetyl, c: N-monochloroacetyl, d: N-acetyl, e: N-ethyl, f: N-allyl, g: N-phenyl) or disubstituted (compounds h: imidazolyl, i: N-diethyl, j: N-diphenyl). Additionally, three N-chlorosulfonyl carbamates are synthesized and used as intermediates for the synthesis of N-unsubstituted compounds b. The accessibility of these compounds is described and compared. Some of the carbamates (1, 4, 5a-j) are used as model compounds for systematic investigations in glycoside syntheses. Selected experimental data (reaction conditions, anomeric ratios, rotation values, selected NMR data) are tabulated.     

DNA synthesis in cultured human fibroblasts: Regulation by 3′ : 5′-cyclic amp

The addition of serum to density-inhibited human fibroblast cultures induced a wave of DNA synthesis, measured as [³H] thymidine incorporation into acid-precipitable material, beginning after 8–12 hr and reaching maximum levels at 16–24 hr. Addition of dibutyryl-3′ : 5′-cyclic AMP (DBcAMP) together with serum inhibited [³H] thymidine incorporation by 75–95%. When DBcAMP was added for the first 4 hr of serum stimulation and then removed, the wave of DNA synthesis was not delayed. This suggested that serum could induce DNA synthesis even though cyclic AMP concentrations were maintained at high levels by DBcAMP during this initial period. These results are inconsistent with the hypothesis that it is the immediate transient reduction in 3′ : 5′-cyclic AMP concentration following the addition of serum that triggers DNA synthesis. By contrast, DBcAMP added 8 hr after serum inhibited [³H] thymidine incorporation to the same extent as DBcAMP added at the same time as serum. This indicated that a step essential for DNA synthesis and occurring late in G₁ was inhibited by high concentrations of 3′ : 5′-cyclic AMP.     

Free flow electrophoresis as a tool for enrichment of mutants with temperature-dependent lethal mutations in lipid A synthesis

Free flow electrophoresis was shown to be a useful tool to enrich for mutants conditionally defective in lipid A synthesis. The method was based on the observation that electrophoretic mobility of bacterial cells is dependent on the structure of lipopolysaccharides and is influenced by lesions in the synthesis of the O-specific chains as well as by lesion in the synthesis of the complete 3-deoxy-D-manno-octulosonic acid (dOclA) lipid A region. Using this procedure a new mutant conditionally defective in dOclA-8-P synthesis was isolated (mutant Ts5). Following a shift to nonpermissive conditions it accumulates a mixture of at least two equally represented lipid A precursor structures. One is made up of glucosamine, phosphate and 3-hydroxymyristic acid in a molar ratio 1.0:1.0:2.0 and lacks dOclA and the nonhydroxylated fatty acids lauric, myristic and palmitic acid. The precursor preparation derived from mutant Ts5 thus differs from previously described lipid A intermediates by the relatively high substitution by palmitic acid. The implications of the above findings to the biosynthesis of lipid A are discussed.     

Fatty acids reverse the cyclic AMP inhibition of triacylglycerol and phosphatidylcholine synthesis in rat hepatocytes.

The influence of cyclic AMP analogues and fatty acids on glycerolipid biosynthesis in monolayer cultures of rat hepatocytes was investigated. Chlorophenylthio-cyclic AMP and adenosine 3':5'-cyclic phosphorothioate inhibited the rate of triacylglycerol synthesis from [1(3)-3H]glycerol, and phosphatidylcholine synthesis from [Me-3H]-choline. Supplementation of the hepatocytes with palmitate (1 mM) reversed chlorophenylthio-cyclic AMP inhibition of triacylglycerol synthesis. Similarly, cyclic AMP analogue-inhibition of phosphatidylcholine synthesis was abolished when the cells were simultaneously incubated with oleate (3 mM). Reactivation of phosphatidylcholine synthesis in chlorophenylthio-cyclic AMP-supplemented cells with oleate was accompanied by conversion of CTP: phosphocholine cytidylyltransferase into the membrane-bound form, since these cells released the enzyme more slowly after treatment with digitonin. The opposing actions of cyclic AMP and fatty acids are discussed in relation to the regulation of glycerolipid biosynthesis during starvation, diabetes and stress.     

Study of the maturation of 5 s RNA precursors in Escherichia coli

The existence of three precursors to 5 s RNA's (p5 s RNA's) has been confirmed. p5 s RNA's and mature 5 s RNA have different 5′-terminal sequences and produce the following 5′-terminal oligonucleotides: p5 s RNA-I:pAUUUG; p5 s RNA-II:pUUUG; p5 s RNA-III:pUUG; 5 s RNA:pUG. The results of experiments on pulse-labelled cells treated with actinomycin D, on chloramphenicol-inhibited cells, on various ribosome assembly-defective mutants and on the state of 5 s RNA in polysomes after a short labelling period, support the following conclusions. (1) p5 s RNA-I is the first identifiable precursor which appears during a pulse. (2) The amount of p5 s RNA-II, relative to those of the other p5 s RNA's, is very low at all times during pulse-chase experiments. On the contrary, it becomes significant during chloramphenicol inhibition and in one assembly-defective mutant under non-permissive conditions. (3) The maturation steps which lead to p5 s RNA-III and 5 s RNA normally occur after binding to 50 s subunit precursor particles and are, consequently, dependent upon protein synthesis. (4) The transition from p5 s RNA-III to 5 s RNA is a slow process, which is neither dependent upon nor required for the proper functioning of 50 s subunits in protein synthesis.     

Effect of Vacuum Ultraviolet Irradiation on Abiogenous Synthesis of Adenine Nucleotides in the Presence of Lunar Ground

Vacuum ultraviolet (VUV) radiation, a powerful energy source in free Space, have been established to promote synthesis of natural nucleotides. It is shown that lunar ground protects from destruction (up to 1.5–2.0% ) the nucleotides formed after VUV-irradiation of dry films (adenosine and inorganic phosphate). Identification and quantitative determination of the products of synthesis and destruction is performed by the method of high performance liquid chromatography. The following products of synthesis are found: 5'-AMP > 2'3'-cAMP > 2'-AMP > 3'5'-cAMP > 3'-AMP. The obtained results are discussed from the viewpoint of hypothesis about the Space (extraterrestrial) origin of biologically important compounds that were initial for evolution on the Earth.     

Network of interactions between unlinked genes: synergistic and antagonistic regulation of iso-1-cytochrome c, iso-2-cytochrome c and cytochrome b2 synthesis]

Five chromosomal genes, CYPI to CYP5 involved in the regulation of the synthesis of iso-1-cytochrome c, iso-2-cytochrome c and cytochrome b2 are described. The function of these genes was studied either by varying the proportion of the mutated and wild type alleles in the cell vy varing the growth conditions, or else by transforming the mutants into sigma-cytoplasmic petites. We have shown a network of genetic interactions which regulate the synthesis of three structurally different proteins : iso-1-cytochrome c, iso-2-cytochrome c and cytochrome b2, by two unlinked genes : CYC1 and CYP1, one of which (CYC1) is the structural gene by iso-1-cytochrome c. Within this network the interactions are proportional to the gene dosage and are either antagonistic or synergistic depending on the allele combination and the protein studied. The mutated alleles cyp1 stimulate the synthesis of iso-2-cytochrome c, inhibit the synthesis of iso-1-cytochrome c, while the cytochrome b2 synthesis is also inhibited but by a combination of cyp1 mutated alleles CYC1 wild type allele. Other loci, CYP2, CYP3, CYP4 and CYP5 were also studied in various allelic combinations. They show some interactions between them or with CYC1 locus but these interactions are different and less pronounced than those involving loci CYP1 and CYC1.