Biomedical subjects

J Pouyet

Publications and source records attributed to J Pouyet.

3 recordsLinked to original sources

PubMed1979

Ethidium bromide binding to core particle: comparison with native chromatin.

Ethidium bromide intercalation into DNA of nuclease digested erythrocyte chromatin and core particle, was followed at low ionic strength by fluorescence measurements, equilibrium dialysis using 14C labelled dye, circular dichroism and electron microscopy. High affinity binding sites in the chromatin are no more present in the core particle, i.e. when the linker is removed. In the case of core particle, a cooperative process occurs, accompanied by a partial stripping of the DNA from the core histone. Finally two populations of core particles can be detected by electron microscopy as far as their binding properties are concerned.

Animals↗

PubMed1978

Ultracentrifugation studies of yeast valyl-tRNA synthetase and of its interaction with tRNAVal.

Yeast valyl-tRNA synthetase and its complexes with yeast tRNAVal were investigated by means of analytical ultracentrifugation. A molecular weight of 125 700 +/- 1500 and a sedimentation coefficient (SO 20, w) of 6.3 +/- 0.3 were found for the native enzyme. When the enzyme (3--60 muM) was mixed with its cognate tRNA, several types of complex were observed, depending on the relative amounts of the two macromolecules. In the presence of equimolecular amounts of tRNA and enzyme, a complex formed by the association of one of each molecule was observed with a sedimentation coefficient of about 7.3 S. However, for tRNA/enzyme stoichiometries lower than one, beside the 1 : 1 complex, a complex of higher molecular weight was observed, with a sedimentation coefficient of about 10.0 S which fits with the association of two valyl-tRNA synthetase molecules with one tRNA molecule. This 2 : 1 complex was predominant from tRNA/enzyme stoichiometries lower than 0.3. It dissociated into the 1 : 1 complex upon addition of monovalent salts or MgCl2, suggesting the electrostatic nature of the interaction in this association. All these association and dissociation phenomena were detected over a large range of pH (6.0--7.5) and in various buffers.

Amino Acyl-tRNA Synthetases↗

PubMed1976

Comparative orientation of the fluorene residue in native DNA modified by N-acetoxy-N-2-acetylaminofluorene and two 7-halogeno derivatives.

Native calf thymus DNA was reacted with N-acetoxy-N-2-acetylaminofluorene (N-AcO-AAF) and its 7-fluoro and 7-iodo derivatives. Different ways of purification of the fluorene modified DNA samples were checked in order ot obtain a nucleic acid free from all noncovalently bound fluorene residues. The decrease in melting temperature in DNA samples modified by N-AcO-AAF(DNA-AAF) was carefully reinvestigated. From these experiments, we conclude that the melting temperature decrease is equal to 1.15 degree C per percent of modified bases, in DNA-AAF samples. Electric dichroism measurements on sonicated DNA samples modified by the different fluorene derivatives show the fluorene ring perpendicular to the helix axis in the case of the N-AcO-AAF and its fluoro derivative, and lying alone the phosphate-sugar backbone in the case of the iodo derivative. The results presented in this paper, along with those obtained earlier, led us to propose an "insertion-denaturation model" for the mode of binding of N-Aco-AAF and its fluoro derivative, and an "outside binding model" for the iodo derivative. Discrepancies with the data obtained by Chang et al.((1974) Biochemistry 13,2142-2148) concerning the melting temperature decrease and the electric dichroism results are observed and discussed.

Acetoxyacetylaminofluorene↗