Construction of hybrid plasmids containing the lysA gene of Escherichia coli: studies of expression in Escherichia coli and Saccharomyces cerevisiae

Summary The lysA gene of Escherichia coli has been cloned from a transducing phage on various plasmids, present in different copy numbers in bacterial cells. Synthesis of the product of this gene, diaminopimelate (DAP)-decarboxylase, and its regulation have been studied. Expression does not follow a simple gene dosage effect, maximal expression already being obtained with a six-copy plasmid. This result suggests that either a positive or an autogenous regulatory mechanism is involved. We also used one of the hybrid plasmids to look for expression of the bacterial lysA gene in Saccharomyces cerevisiae. The results indicate that the product of the E. coli gene is not actively translated in yeast.     

The relA locus and the regulation of lysine biosynthesis in Escherichia coli

Summary The allelic state of relA influences the phenotype of Escherichia coli strains carrying the lysA22 mutation: lysA22 relA strains are Lys^– where lysA22 relA ⁺ strains grow (slowly) in the absence of lysine. This physiological effect has been related to an effect of the expression of the relA locus on the regulation of lysine biosynthesis. The fully derepressed levels of some lysine enzymes (aspartokinase III, aspartic semialdehyde dehydrogenase, dihydrodipicolinate reductase) are observed under lysine limitation only in rel ⁺ strains. And the induction of DAP-decarboxylase by DAP is much higher in rel ⁺ than in rel ^– strains when an amino acid limitation of growth is also realised. These results are in agreement with the hypothesis of Stephens et al. (1975) on a possible role of the stringent regulation as a general signal for amino acid deficiency.     

Iron-porphyrin catalysis of the oxidative dealkylation of para-nitro-anisole and 7-ethoxycoumarin by cumylhydroperoxide: a possible model for the corresponding cytochrome P 450-dependent reactions

A biphasic system containing an iron porphyrin, Fe (TPP) (C1)¹ or [Fe(TPP)]₂O, efficiently catalyzes the cumyl-or tertiobutyl-hydroperoxide-supported dealkylation of p-nitroanisole and 7-ethoxycoumarin to the corresponding phenol and formaldehyde. Stoichiometric amounts of iron porphyrin and hydroperoxide give a quantitative reaction. Catalytic amounts of iron porphyrin give reaction rates and yields which are proportional to substrate concentration. With increasing hydroperoxide concentrations, the rates level offto limit values and the yield rapidly decreases. The maximum rates obtained approach those of the reactions mediated by cytochrome P 450-dependent monooxygenases.     

Immunohistochemical localization of a gastrin-like peptide in the brain of an amphibian,Xenopus laevis Daud.

Summary The indirect immunofluorescence technique was used to demonstrate a substance reacting with gastrin antisera in the brain of Xenopus laevis.Immunoreactive material was found in two sites: (1) In the caudal hypothalamus more precisely in the nucleus infundibularis ventralis, (NIV) of the pars ventralis of the tuber cinereum, (PVTC). The fluorescent axons of the reactive parikarya of the NIV give rise to two symmetrical tracts which run rostro-ventrally and join, in the infundibular floor, the preoptico-hypophysial tract, where they form an uneven median tract coursing caudally and running along the medio-tuberal area before entering the external zone of the median eminence. (2) In the anterior preoptic area (APOA), where numerous nerve fibers and endings form a dense network near the preoptic recess. The exact origin of these terminals has not yet been determined.Control of immunohistochemical specificity shows that the labeling by gastrin antisera is suppressed by gastrin (2–17), but also by cholecystokinin (CCK) and pentagastrin (Peptavlon). These results indicate that the immunoreactive substance revealed belongs to the gastrin group and has an antigenic determinant composed of the amino acid sequence or a portion thereof common to gastrin, CCK and Peptavlon (Trp-Met-Asp-Phe).It should be emphasized that, in the brain of Xenopus laevis, both gastrinimmunoreactive sites correspond to the sites of uptake of steroid hormones (Kelley et al., 1975; Morrell et al., 1975).Supported by the D.G.R.S.T., Contrat n 77.7.0648     

Réflexions critiques sur l'écologieet la systématique des Lingules actuelles et fossiles

New topics on ecology and systematics of recent and fossil Lingulids lead to an obvious revision of our knowledges on this zoological group. At first, the recent species need systematics and taxonomy on the bases of new described specific criteria (as, morphology of deltidial areas, muscle disposition); the results are briefly indicated. But, in fossil species, disorder and disparity of used characteristics are emphasized.The general conceiving on ecology of Lingulids are reviewed and discussed, especially on bathymetry and salinity; sediment and oxygenation conditions; taphocoenosis and lingulid «communities. On recent species, all these points are also studied, especially some ecological requirements (salinity, bathymetry, grain size), and mechanism of burrowing ability, burrow living positions in the sediments, as shell preservations after death and fossilization, to facilitate the paleobiotope interpretations. Recent animals are euryhalin, surviving at salinities from about 13 to 42‰; they could be considered as well adapted to waters with strong salinity fluctuations. They show preference to fine sand bottoms (lowest particle size about 40–60 μm). Their bathymetric distribution occurs between 0 and about 500 m (Lingula especially between 5–50 m; Glottidia 15–70 m). The isotherms 8–10°C seem to restrict their geographical and bathymetric distribution.Therefore, some post-palaeozoic lingulid bedsare studied or redescribed on the bases of the above discussed characteristics, and new interpretations on the environmental situation are given (Trias of Vosges Mountains; Oligocene from Japan; Eocene of London Basin). More caution must be used in study of fossil Lingulids that are not especially animals living in infralittoral bottoms with low salinity and deficient oxygenation, as generally accepted.     

Mitochondrial protein alteration in active brown fat: A sodium dodecyl sulfate-polyacrylamide gel electrophoretic study

The polypeptide composition of mitochondria isolated from the brown adipose tissue of control rats (bred at 22°C) or cold-exposed animals (bred at 6°C) was compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A striking increase in the content of an unknown polypeptide (apparent molecular weight 32,000 daltons) was found after cold adaptation, a phenomenon which was reversed during re-adaptation to a normal temperature. This protein seems to be localized in the membrane fraction of the mitochondria.     

Régulation et signification physiologique de l'aspartate-ammonium lyase (aspartase) de Pseudomonas fluorescens type R

The biosynthesis of aspartate-ammonium lyase, the enzyme which is induced by aspartic acid, is specifically repressed by fumaric acid. In the presence of aspartate, the enzyme permits the deamination of this compound by the cell. Aspartic acid is converted into fumaric acid which is an intermediate in the Krebs'cycle. The reaction may be considered as an anaplerotic sequence. In the absence of aspartic acid in the culture medium, its role is anabolic; the enzyme catalyses the biosynthesis of this amino acid. Therefore it appears that the reversible reaction fumarate+NH₃=aspartate catalysed by aspartase is included in amphibolic processes.