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F Caron

Publications and source records attributed to F Caron.

88 records · Page 5Linked to original sources
PubMed1984

Theoretical study of the geometrical arrangement of GT and GA wobble pairs in two short duplexes, Proton NMR chemical shifts and interaction energy calculations.

NMR shielding constants are calculated for the base protons of duplexes formed by the dodecamer d(CGTGAATTCGCG) and the decamer d(CCAAGATTGG). A good agreement with experimental data is obtained for B-DNA helices in which the wobble GT and GA pairs are in the plane of the corresponding GC pairs of the parent duplexes formed by d(CGCGAATTCGCG) and d(CCAAGCTTGG), if the glycosyl bonds of T and G or A and G are symmetrical with respect to the dyad axis of the Watson-Crick GC pair. Interaction energy calculations show that this type of geometrical arrangement, which implies a distortion of the ribonphosphate backbone of both strands of the duplexes are more stable than those in which only one strand has its conformation modified by the presence of the wobble pair. For the duplex containing the GA pair, NMR chemical shifts as well as interaction energy computations favour the Watson-Crick hydrogen bonding scheme. The variation of the different contributions (intrastrand, interstrand, pair-pair) to the interaction energy between the bases of the duplexes, with the geometrical arrangement of the wobble pairs, is reported.

Base Composition↗
PubMed1984

Blocking of in vitro translation of Paramecium messenger RNAs is due to messenger RNA primary structure.

Paramecium primaurelia mRNAs were translated in vitro in rabbit reticulocyte lysate and the products of translation were analyzed by their size. We show that the large majority of these products are of short but discrete sizes irrespective of the length of the mRNA which directs their synthesis. An illustrative example is given by the translation of mRNA of G surface antigen which directs the synthesis of a 50 kD polypeptide instead of the complete 250 kD protein. Control experiments suggest that the blocking is due to mRNA primary structure.

Animals↗
PubMed1979

Characterization of a histone-like protein extracted from yeast mitochondria.

Analysis of proteins isolated by affinity chromatography on DNA-cellulose from highly purified yeast mitochondria shows that these organelles do not contain histones but have in abundance a DNA-binding protein of 20,000 daltons. The purification yield of this protein, called HM, indicates that mitochondria have at least an equal mass of HM relative to DNA. The amino acid composition and its electrophoretic characterization reveal that HM, rich in lysine, is slightly basic and heat stable. HM appears to be coded by the yeast nucleus, as shown by its presence in several "petite" mutants. We have shown that HM, like histones or histone-like proteins, is able to introduce superhelical turns into circular relaxed DNA in the presence of a nicking-closing activity.

Amino Acids↗
PubMed1978

The influence of protein-lipid interactions on the order-disorder conformational transitions of the hydrocarbon chain.

The phases of simple systems involving one type of protein (lysozyme or cytochrome c) and one type of lipid (phosphatidic acid) have been characterized by X-ray crystallography, chemical analysis and spin-labeling technique as a function of temperature. They are of the lamellar type with alternative protein monolayers and lipid bilayers. According to the pH, two types of lamellar phases are obtained, one where the lipid-protein interactions are mainly hydrophobic, the other where they are electrostatic. In both cases, a phase transition occurs as temperature is lowered, between a high temperature phase, where all the lipids are in the liquid-like state, and another phase where some lipid chains are rigid. In the case of the phases with electrostatic interaction, it is shown that the onset of the order-disorder transition is shifted towards low temperature as compared with the homologous lipid-water phase and that the protein content of the phase decreases as the ratio of the liquid to rigid hydrocarbon chains decreases. This leads us to suggest that in the systems studied in this work the proteins interact only with lipid in the liquid-like state. In the case of the phases with hydrophobic interaction, it is shown that the extent of hydrophobic interaction between protein and lipid increases as the unsaturation of the hydrocarbon chains increases. The onset of the order-disorder transition shows a greater shift towards low temperature than the one observed in the case of the phase with electrostatic interaction.

Cytochrome c Group↗
PubMedDate not supplied

Irreversible trapping of DNA during crossed-field gel electrophoresis.

Using an original protocol with a rotating gel electrophoresis apparatus, it is shown that duplex DNA undergoing crossed-field electrophoresis in agarose gets trapped in the gel when the field is increased above a threshold value which decreases with the chain length and depends on the angle between the fields in a non-monotonous manner. This trapping is irreversible, i.e. once trapped at a high field strength, chains are unable to resume their motion when the field is returned to a lower value at which they moved prior to trapping. A model of trapping by "tight knots" is proposed. It predicts a trapping threshold proportional to the inverse square of the electric field, in qualitative agreement with the data. The implications of our results for the separation of large DNA molecules are discussed.

Chromosome Banding↗
PubMedDate not supplied

Does Paramecium primaurelia use a different genetic code in its macronucleus?

It has long been known that messenger RNAs (mRNAs) of ciliates and in particular of Paramecium are not translated well in heterologous in vitro translation systems. Recently, we have demonstrated for Paramecium primaurelia that this phenomenon results from the presence of well-defined blocking sites in the coding sequences of almost all mRNAs, and that these sites are an intrinsic feature of the primary as opposed to the secondary structure of the mRNAs. Here we show that both the gene and the mRNA for the G surface antigen of P. primaurelia contain numerous TAA and TAG codons scattered throughout their coding sequences. We propose that these codons do not represent termination codons in P. primaurelia but instead code for glutamic acid or glutamine and that the in vitro translation of Paramecium mRNAs is blocked by their presence.

Animals↗
PubMedDate not supplied

A method for the amplification of Paramecium micronuclear DNA by polymerase chain reaction and its application to the central repeats of Paramecium primaurelia G surface antigen genes.

This paper describes a method which allows the amplification of Paramecium micronuclear DNA. Amacronucleate cells are first obtained by an appropriate treatment with nocodazole, a microtubule depolymerizing agent which blocks the elongation of the macronucleus and the distribution of the micronuclei at cell division between the two daughter cells; then, DNA from such cells is amplified by the polymerase chain reaction technique. We have applied this method to the problem of the central repeats of the G surface antigen of P. primaurelia (strain 156). The central repeats consist of a 74 amino acid sequence repeated in tandem. The sequence identity of these repeats is also found in the nucleotide sequence even at silent codon positions, suggesting the existence of a mechanism of identity maintenance acting at the nucleotide level. Mechanisms based on RNA secondary structure which are frequently proposed as an explanation of this phenomenon are unlikely to be valid in this case. One can, therefore, imagine that these repeats might originate from one micronuclear sequence through duplicative processes which could occur during the formation of the macronucleus. We have used the described technique to amplify the micronuclear version of the central repeats and showed that it is identical to the macronuclear version, thus ruling out the above hypothesis. Therefore, intragenic recombination appears to be the most likely explanation of the sequence identity of these central repeats.

Amino Acid Sequence↗
PubMedDate not supplied

[Bismuth revisited in Helicobacter pylori gastro-duodenal infection].

The various hypothesis for the explantation of reversible bismuth encephalopathy are reviewed and discussed. Today, this side effect appears to be devoid of mystery, due to uncontrolled and inhibited ingestion of bismuth salts which increased the emergence of genetic and physiopathologic risk factors and brought about the cases of neurotoxicity. Bismuth therapy has shown major efficacy in the treatment of gastroduodenal ulcers. Colloidal bismuth subcitrate is as effective as the H2-receptor antagonists in peptic ulcer. In addition, it offers a lower rate of relapse. This therapeutic benefit has been attributed to a cytoprotective and demulcent action. Moreover bismuth acts as an antimicrobial agent, suppressing the organism Helicobacter pylori which occupies a central place in contemporary views on pathophysiology of ulcer disease. Side effects so far reported have been very infrequent mild and transient when the drug is used at low dosage providing blood-bismuth concentration above toxic values. Colloidal bismuth subcitrate complies to the requirements for a modern drug insofar as it is prescribed in period no longer than 6-8 weeks, followed by 8 weeks bismuth-free intervals.

Bismuth↗