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Biomedical subjects

J Huet

Publications and source records attributed to J Huet.

64 records · Page 4Linked to original sources
PubMed1975

Dissociation of two polypeptide chains from yeast RNA polymerase A.

Yeast RNA polymerase A (RNA nucleotidyltransferase; nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6) can be converted to a new form of enzyme, called RNA polymerase A*, which is lacking two polypeptide chains of 48,000 and 37,000 daltons. Apart from these two missing polypeptides the subunit structures of RNA polymerases A and A* are indistinguishable. RNA polymerase A* differs from the complete enzyme in its electrophoretic and chromatographic behavior, template requirements, and alpha-amanitin sensitivity. RNA polymerase A* transcribes the alternated copolymer d(A-T)n with the same efficiency as RNA polymerase A but its specific activity is greatly reduced with native calf thymus DNA as template. The transcription of a variety of synthetic templates is also altered by removal of the two polypeptide chains. RNA polymerase A* is inhibited by high concentrations of alpha-amanitin (500 mug/ml), whereas RNA polymerase A is comparatively less sensitive to the toxic peptide. The data are discussed in terms of possible roles of the two dissociable polypeptides.

Amanitins↗
PubMed1975

Dominant and semidominant mutations leading to thermosensitivity of ribonucleic acid biosynthesis in Saccharomyces cerevisiae.

Different dominant thermosensitive mutations affecting the same gene were selected in Saccharomyces cerevisiae. Ribonucleic acid (RNA) synthesis decreased rapidly and markedly at 37 C in all the mutants whether they were in a homozygous or a heterozygous state. Protein biosynthesis was at first unaffected and then decreased slowly, stopping after 5 h. Measurements of RNA biosynthesis in isolated nuclei as well as in vitro activities of RNA polymerases A and B at 22 and 37 C failed to reveal any difference between mutants and the wild type. Analysis of the nature of the residual RNAs synthesized at the high temperature in the mutants showed a small relative increase in the messenger RNA fraction, but it was not sufficient to indicate a specific inactivation of RNA polymerase A activity. The results suggest an impairment in a common regulatory element for all RNA polymerases acting at the level of the initiation of transcription. Similar mutants with a semidominant phenotype were obtained in which the lesions were in two other unlinked loci.

Antifungal Agents↗
PubMed1975

[Effects of ethinyl estradiol compared with norethisterone (pure or contaminated) on vaginal keratinization of castrated rats].

Norethisterone samples are often contaminated by estrogen traces which can be measured by mass spectrometry and which invest the progestative with estrogenic properties in the Allen and Doisy test. Therefore, one had better, in pharmacodynamic experimenting, use samples that have been purified by chromatography or that are pure out of synthesis. However, one will not forget these are not without some estrogenicity, a fact which seems linked to the very nature of the norethisterone molecule.

Animals↗
PubMed1972

Mitoribosomes from Candida utilis. Morphological, physical, and chemical characterization of the monomer form and of its subunits.

Highly purified mitochondrial ribosomes (mitoribosomes) have been obtained from the yeast Candida utilis. Sedimentation analysis in sucrose gradients made in 5 mM MgCl(2), 1 mM Tris, pH 7.4 and 50 mM KCl clearly distinguishes mitoribosomes (72S) from cytoplasmic ribosomes (cytoribosomes) (78S). Mitoribosomes are completely dissociated into 50S and 36S subunits at 10(-4)M MgCl(2) whereas complete dissociation of cytoribosomes into 61S and 37S subunits occurs only at 10(-6)M MgCl(2) Electron microscopy of negatively stained mitoribosomes (72S peak) shows bipartite profiles, about 265 x 210 x 200 A Characteristic views are interpreted as frontal, dorsal, and lateral projections of the particles, the latter is observed in two enantiomorphic forms Mitoribosome 50S subunits display rounded profiles bearing a conspicuous knoblike projection, reminiscent of the large bacterial subunit. The 36S subunits show a variety of angular profiles. Mitoribosomal subunits are subject to artifactual dimerization at high Mg(2+) concentration Under these conditions, a supplementary 80S peak arises. Electron microscopic observation of the 80S peak reveals closely paired particles of the 50S type Buoyant density determinations after glutaraldehyde fixation show a single peak at rho = 1.48 for mitoribosomes and 1.53 for cytoribosomes In the presence of ethylenediaminetetraacetate (EDTA), two species of RNA, 21S and 16S, are obtained from mitoribosomes, while 25S and 17S RNA are obtained from cytoribosomes It is established that the small and large RNA species are derived from the 36S and 50S subunits, respectively, by extraction of the RNA from each subunit The G + C content of the RNA is lower for mitoribosomes (33%) than for cytoribosomes (50%). Incubation of C utilis mitochondria with leucine-(14)C results in the labeling of 72S mitoribosomes. The leucine-(14)C incorporation is inhibited by chloramphenicol and resistant to cycloheximide Puromycin strips the incorporated radioactivity from the 72S mitoribosomes, which is consistent with the view that leucine-(14)C is incorporated into nascent polypeptide chains at the level of mitoribosomes

Adenine↗
PubMedDate not supplied

Inhibition of tumor growth and polyamine uptake by tetracyclic amidines bearing a putrescine moiety.

Tetracyclic amidines (tetrahydroquino[4.3-b][l]benzazepine: compound 11 and tetrahydrobenzo[k]naphthyridine: compound 12) bearing a putrescine moiety possess significant DNA-binding affinity. We report here that these compounds and their a and b isomers inhibit tumor cell growth and putrescine uptake in 3LL carcinoma cells in vitro. Moreover, compound 11 reduced by 50% the accumulation of putrescine in intestinal brush border membrane vesicles. In CHO-MG, a cell line deficient for the specific polyamine uptake system, the cytotoxicity of these compounds was significantly reduced compared to the CHO wild cell line. The IC50 for CHO-MG was significantly higher than for CHO, demonstrating that the polyamine transport system increased the efficacy of these compounds. The efficacy of compounds 11 and 12 might therefore be related to their ability to interact with DNA as well as their structural analogy with polyamines. Moreover, we clearly show that DFMO enhances the efficacy of these tetracyclic amidines in vivo. Potential mechanisms include: a) lower intracellular polyamine levels reduces polyamine DNA-stabilizing functions, increasing accessibility for DNA-binding drugs; b) DFMO enhances the polyamine uptake system in tumor cells, increasing the entry of tetracyclic amidines bearing a putrescine moiety as well as their accessibility to final DNA-binding sites. The fact that natural polyamine uptake is reduced by the same compounds constitutes an additive mechanism for antitumoral efficiency.

Amidines↗