Etude des proteines an cours de la germination des graiues: Isolement et analyse des histories de radis Par

Histories of radish seedlings liave been characterised by comparison with pea histones extracted and purified under the same conditions. Submitted to acrylamide gel analysis the radish histones are resolved into main protein bands comparable to those of pea or calf thymus histones. However, protein bands of lesser importance which are not to be found in electrophoretic profils of pea or calf thymus histones, appear together with the main bands of radish histones. Study of these supplementary proteins through isoelectric focusing makes it possible to distinguish two groups: contaminating acid proteins and weakly basic proteins characterised by their high amide content.     

In vitro synthesis and repression of argininosuccinase in Escherichia coli K12; partial purification of the arginine repressor

Summary 80dargECBH DNA has been used to direct cell-free synthesis of argininosuccinase, the argH gene product in Escherichia coli K12. In vitro enzyme synthesis is sensitive to repression by partially purified preparations from an argR ⁺ strain but not by corresponding preparations from an argR ^- strain. Using DNA-cellulose chromatography, approximately seventyfold purification of repressor has been obtained. The partially purified preparation represses argininosuccinase synthesis but has no effect on -galactosidase synthesis.     

Membrane reconstitution in CHL-R mutants of Escherichia coli K 12 V. ATPase incorporation into particles formed by complementation

Mechanical treatments of cell suspensions of Escherichia coli K 12 strain PA 601, and its two mutants chl A⁻ and chl B⁻, in a buffer without Mg²⁺ lead to partial solubilization of membrane-bound ATPase. After ultracentrifugation of cell-free extracts, ATPase can be recovered in the soluble fraction. Contrary to membrane ATPase, the soluble enzyme has the following properties: (1) it is insensitive to N,N′-dicyclohexylcarbodiimide; (2) heat-inactivation kinetics show a reactivation in the first 3 min and the half-time is 15 min; (3) ADP is a substrate. In the course of complementation between soluble fractions of mutants chl A⁻ and chl B⁻, a part of soluble ATPase is incorporated into the newly formed particles. The specific activity of these particles is nearly the same as that of native particles; the ATPase bound to native membrane and the ATPase bound to the newly-formed particles both have the same biochemical properties.     

大肠杆菌碱性磷酸酶的体外定向进化研究

大肠杆菌碱性磷酸酶（E.coli alkaline phosphatase, EAP, EC 3.1.3.1）是一个非特异性二聚体磷酸单酯酶. 采用易错聚合酶链反应(error prone PCR)的方法,在原有高活力突变株的基础上,对EAP远离活性中心催化三联体的区域进行定向进化,经两轮error prone PCR,获得催化活力较亲本D101S突变株提高3倍、较野生型酶提高35倍的进化酶4-186,并对该酶的催化动力学特征进行了分析. 进化酶基因的DNA测序表明4-186含两个有义氨基酸置换：K167R和S374C,二者既不位于底物结合位点,也不位于酶的金属离子结合位点.     

Membrane reconstitution in chl-r mutants of Escherichia coli K 12 VI. Morphological study of membrane assembly during complementation between extracts of chl-r mutants

The particles formed during the complementation between supernatant extracts of mutants chl A⁻ and chl B⁻ of Escherichia coli K 12 have been examined under the electron microscope. These particles look like membranous formations with a vesicular structure limited by a triple-layered membrane. The observations made on these particles at various incubation times during complementation show that the aggregation progresses through several stages of organization. When the phenomenon becomes steady, the population of reaggregated particles shows a large structural heterogeneity: it consists of small aggregates, filaments and particulary well-organized closed vesicles. As we had previously shown for the reconstitution of nitrate reductase, the rate of formation and the structure of newly formed aggregates depend on various parameters (temperature, dialysis).     

Relation entre structure, composition et fractionnement par le Triton X-100 de la lamelle chloroplastique de la souche sauvage et de deux mutants non photosynthetiques de Chlamydomonas reinhardti

Relationship of structure, composition and Triton X-100 fractionation of chloroplas lamellae in wild type and two non-photosynthetic mutant strains of Chlamydomonas reinhardti

In order to provide information on the link between the two photosystems studies on the mode of action of Triton X-100 has been carried out on mutants, strains ac 21, Fl 15 and wild type of Chlamydomonas reinhardti. Experiments show that the release of Photosystem I particles from mutant chloroplast fragments needs less Triton X-100 than wild type does and that, compared to wild type, the chloroplast fragments of mutants appear to be deficient in carotenoids (ac 21) or in lipids (Fl 15). It is possible, therefore, to correlate the easier splitting of the mutant membrane by detergent with a decrease in the amount of these compounds (carotenoids and lipids) in mutant strains.

The following interpretation is proposed: (a) some of the carotenoids could be part of the hydrophobic sites on Photosystem I subchloroplast particles; (b) some polar lipids could be linked to these sites; (c) Triton X-100 could, in a competitive way, replace the membrane lipids linked to the hydrophobic sites of subchloroplast particles. It seems probable that anomalies in the mutant behaviour in regard to the Triton X-100 action are related to membrane structural defects in these mutants.     

Regulatory mutants of dihydrofolate reductase in Escherichia coli K12

Summary Trimethoprim inhibits dihydrofolate reductase. Mutations conferring trimethoprim-resistance on E. coli K12 result in either an altered reductase with decreased affinity for the drug, or in 2–30 fold higher levels of the enzyme. Studies of the latter class of mutants indicate that dihydrofolate reductase is regulated by a diffusible molecule, and is probably under negative control. The regulatory mutants, some of which are temperature-sensitive, act cis.     

Uvm mutants of Escherichia coli K 12 deficient in UV mutagenesis

Summary Selection for defective reversion induction, after UV treatment of E. coli K 12, yielded uvm mutants. These mutants exhibited highly reduced or no UV mutability for all loci tested although they were moderately and normally mutable by X-rays and EMS, respectively. Uvm mutations confer only a slight sensitivity to killing by UV and X-rays and no clear sensitivity to the lethal effect of HN2, EMS or MMS. Growth and viability of untreated uvm cells were normal. The properties of uvm mutants are discussed in relation to those of other relevant mutant types and to some actual problems of induced mutagenesis.     

Uvm mutants of Escherichia coli K12 deficient in UV mutagenesis

Summary Uvm mutants of Escherichia coli K12 selected for defective UV reversion induction have previously been reported to differ considerably from the UV-reversion-less recA and lexA mutants with regard to survival or mutagenic response to UV, X-rays and alkylating agents. In the present study, the phenotypic characterization of uvm mutants was extended to investigate several cellular processes which also may be related to or involved in UV mutagenesis. Like recA and lexA mutations, the uvm mutations exhibit highly reduced Weigle reactivation and normal host cell reactivation of UV irradiated phage . But unlike recA and lexA, the uvm mutations do not impair genetic recombination, UV induction of prophage or R plasmid-mediated UV resistance and mutagenesis. These phenotypical characteristics and preliminary results of genetic mapping lend further support to the assumption that the uvm site may be a novel locus affecting, apart from the recA and lexA loci, the error-prone repair pathway in E. coli.     

In vitro assembly of Ebola virus nucleocapsidlike complex expressed in E. coli

Ebola virus (EBOV) harbors an RNA genome encapsidated by nucleoprotein (NP) along with other viral proteins to form a nucleocapsid complex. Previous Cryoeletron tomography and biochemical studies have shown the helical structure of EBOV nucleocapsid at nanometer resolution and the first 450 amino-acid of NP (NPΔ451–739) alone is capable of forming a helical nucleocapsid-like complex (NLC). However, the structural basis for NP-NP interaction and the dynamic procedure of the nucleocapsid assembly is yet poorly understood. In this work, we, by using an E. coli expression system, captured a series of images of NPΔ451–739 conformers at different stages of NLC assembly by negative-stain electron microscopy, which allowed us to picture the dynamic procedure of EBOV nucleocapsid assembly. Along with further biochemical studies, we showed the assembly of NLC is salt-sensitive, and also established an indispensible role of RNA in this process. We propose the diverse modes of NLC elongation might be the key determinants shaping the plasticity of EBOV virions. Our findings provide a new model for characterizing the self-oligomerization of viral nucleoproteins and studying the dynamic assembly process of viral nucleocapsid in vitro.     

Etude des paraios de levures du genre rhodotorula IV. variation de la teneur en chitine

A study of the chitin contents in Rhodotorula yeast walls indicates that the contents of this amino polysaccaharide may vary from 0.58 to 12% according to the yeast and depending on the culture conditions.The variations of the glucosamine concentrations, estimated by direct determinations on the cell walls, do not reflect the modifications of the chitin contents.Depending on the culture conditions, the yeast cell walls possess structures which are differently degraded by enzyme actions. Cell walls with high glucosamine content, but low amino-acids content, are the more easily degraded.     

Evidence of abortive recombination in ruv mutants of Escherichia coli K12

Summary Genetic recombination in Escherichia coli was investigated by measuring the effect of mutations in ruv and rec genes on F-prime transfer and mobilization of nonconjugative plasmids. Mutation of ruv was found to reduce the recovery of F-prime transconjugants in crosses with recB recC sbcA strains by about 30-fold and with recB recC sbcB sbcC strains by more than 300-fold. Conjugative plasmids lacking any significant homology with the chromosome were transferred normally to these ruv mutants. Mobilization of the plasmid cloning vectors pHSG415, pBR322, pACYC184 and pUC18 were reduced by 20- to 100-fold in crosses with ruv rec ⁺ sbc ⁺ strains, depending on the plasmid used. Recombinant plasmids carrying ruv ⁺ were transferred efficiently. With both F-prime transfer and F-prime cointegrate mobilization, the effect of ruv was suppressed by inactivating recA. It is proposed that the failure to recover transconjugants in ruv recA ⁺strains is due to abortive recombination and that the ruv genes define activities which function late in recombination to help convert recombination intermediates into viable products.     

Etude et mise au point d'une methode permettant de mesurer l'activite des tetrathionate-reductases d'origine bacterienne. Inhibition par l'oxygene de la biosynthese et de l'activite de l'enzyme d'Escherichia intermedia

Summary A method is described which permits the measurement of the tetrathionate reductase activity of bacterial extracts. In anaerobic cultures the reductase is an inducible enzyme. In aerobic cultures its formation is completely repressed by oxygen. In a suspension of resting cells atmospheric oxygen inhibits reversibly the activity of the reductase.      

Etude comparee de la detection chimique des proies par Proteus anguinus,cavernicole, et son parent de surface Necturus maculosus (proteidae,urodela)

Do the blind cave salamander Proteus and its epigean relative Necturus use the chemical sense in searching for prey? Proteus shows a significant, and Necturus only a weak, preference for water which passes living prey before entering a choice chamber. Prey which was frozen before the test also gave the same result in both species. However, with this immobilized prey the time for a decision in the test was much longer. The results of ten series of tests demonstrate the importance of chemoreception for prey detection in Proteus. The weaker reactions in Necturus can be explained probably by the different biotope.Six other series of tests have been conducted to show that our results are not influenced by stimuli relating to mechanoreception, thigmotaxis and rheotropism.     

cysB and cysE mutants of Escherichia coli K12 show increased resistance to novobiocin

Summary Mutations in the cysB and cysE genes of Escherichia coli K12 cause an increase in resistance to the gyrase inhibitor novobiocin but not to coumermycin, acriflavine and rifampicin. This unusual relationship was also observed among spontaneous novobiocin resistant (Nov^r) mutants: 10% of Nov^r mutants isolated on rich (LA) plates with novobiocin could not grow on minimal plates, and among those approximately half were cysB or cysE mutants. Further analyses demonstrated that cysB and cysE negative alleles neither interfere with transport of novobiocin nor affect DNA supercoiling.     

Synchronous division induced in Escherichia coli K12 by gemts mutants of phage Mu

Summary Infection with the bacteriophage mutant Mu c ⁺ gemts2 at 42° C induces synchrony in cell division in cultures of Escherichia coli K12. This synchrony may last for several cycles and is not only due to selection since synchronization is observed even when bacterial survival to the infection is over 80% as in lysogens for Mu c ⁺ gemts2. The mechanism by which sycnhrony is induced is not known, but since the product of Mu gene gem (previously called lig) has been shown to interact with the enzymatic system in the bacteria controlling the degree of DNA supercoiling, the phenomenon could be a consequence of this interaction.     

Chronostratigraphie de la fin de la derniere glaciation,a la lumiere des resultats de l'etude lithostratigraphique et palynologique du site de Maisieres-Canal (Belgique)

The upper part of the palaeoclimatic sequence of Maisières-Canal shows a succession of four mild episodes at thetransition between the Pleniglacial and the Late-Glacial. Those four mild fluctuations are respectively correlated with Langerie, Lascaux, Angles-sur-l'Anglin and Pré-Bölling oscillations.