The dead-arm evolution of river systems: A comparison between the information provided by living Copepoda and Cladocera populations and by Bosminidae and Chydroidae remains

Methodological investigations, using remains of Bosminidae and Chydoridae, were undertaken to study the development of ecosystems in former river channels. Four biotopes from two former channels of different ages were used in this work. The Copepoda and Cladocera populations characterized each of the 11 sampling stations in relation to ecological factors, which are linked to the development stage in each ecosystem. Analysis of only the Bosminidae and Chydoridae populations presented practically the same information as an analysis of the total populations of Copepoda and Cladocera. The distribution of Bosminidae and Chydoridae remains taken from the surficial sediments at the deepest point of each former channel strongly resembled the distribution of the living populations sampled at several stations during one full year. Therefore, Bosminidae and Chydoridae remains could provide us with pertinent information concerning each phase of ecological succession that occurs in abandoned river channels.     

The X-ray induced G2 arrest in mouse eggs: a maternal effect involving a lack of polypeptide phosphorylation

Summary In some strains of mice, eggs when X irradiated during the pronuclear stage, undergo a mitotic block in the G₂ phase of the first cell cycle and cleave when the second division takes place in controls. The importance of this effect varies considerably with the strain and depends exclusively on the maternal genotype. In previous work, two-dimensional electrophoresis showed that eggs blocked at the one-cell stage after irradiation, undergo the same modifications in polypeptide synthesis as two-cell controls of the same age, except at the time of normal first mitosis, where three polypeptide sets of 30, 35 and 45 kDa appear only in cleaving controls. In the present study, we have found phosphorylations in dividing controls, on polypeptides of 30, 35 and 45 kDa. These phosphorylations are not seen in blocked irradiated eggs.     

Sequence analysis of a Dictyostelium discoideum gene coding for an active dihydroorotate dehydrogenase in yeast

A Dictyostelium discoideum DNA fragment isolated on the basis of its ability to complement the ural mutation of yeast, codes for a dihydroorotate dehydrogenase activity. The complete nucleotide sequence of this 1898 bp fragment has been determined and reveals an open reading frame capable of coding for a 369 amino acid polypeptide of molecular mass 47.000. The gene shows preferential use of codons with weak pairing forces. Eleven codons, mainly those with a G in the third position, are absent. The flanking sequences are unusually rich in A + T (80%). Several direct and inverted repeats exist in the 5' flanking sequence.     

Studies in vitro on mouse-egg radiosensitivity from fertilization up to the first cleavage

Super-ovulated eggs from the Balb/c strain were incubated, at various times after injection of HCG, in Whitten's medium containing tritiated thymidine. They were fixed on the following day at the 2-cell stage and prepared for autoradiography. On the basis of the results, pregnant mice were irradiated with various doses of X-rays at 15 h post HCG (fertilization), 19 h (phonuclear stage before DNA synthesis), 24 h (maximal DNA synthesis) and 27.5 h (DNA synthesis completed). On the day following irradiation, embryos were collected and classified into incleaved or 2-cell embryos, and development of the 2-cell embryos was followed in culture.

Irradiation was most effective when administered at 19 h after injection of HCG. Such a treatment increased the mortality before the first cleavage and, thereafter, from the 8-cell (100 rad) or morula stage (25, 50 rad). Blastocyst hatching and implantation were also impaired. Irradiation at other times was much less harmful for the embryos, which died mainly from the blastocyst stage. Finally, radiosensitivities of the mouse zygote at the various times studied can be estimated as follows: fertilization, + + +; pronuclear stage before DNA synthesis, + + + + +; maximal DNA synthesis, +; DNA synthesis terminated, + +.     

Use of flow cytometry in oenology to analyse yeasts

Flow cytometry is a rapid method with many microbiological applications. This technique can be used to obtain counts of viable yeasts in 30 min, whereas a 48 h incubation is necessary with plate counts. This rapid method was tested for its suitability to analyse wine yeasts in a multicentre study in our three laboratories. The study compares measurements obtained by flow cytometry and the usual method, in order to test the reliability of the new method. The results obtained were very similar in terms of both the micro-organisms detected and the precision of measurements.     

In Xenopus laevis, the product of a developmentally regulated mRNA is structurally and functionally homologous to a Saccharomyces cerevisiae protein involved in translation fidelity.

We have performed a differential screen of a Xenopus egg cDNA library and selected two clones (Cl1 and Cl2) corresponding to mRNA which are specifically adenylated and recruited into polysomes after fertilization. Sequence analysis of Cl1 reveals that the corresponding protein is 67.5% identical (83% similar) to the product of the Saccharomyces cerevisiae SUP45 (also called SUP1 or SAL4) gene. This gene, when mutated, is an omnipotent suppressor of nonsense codons. When expressed in a sup45 mutant, the Xenopus Cl1 cDNA was able to suppress sup45-related phenotypes, showing that the structural homology reflects a functional homology. Our discovery of a structural and functional homolog in Xenopus cells implies that the function of SUP45 is not restricted to lower eukaryotes and that the SUP45 protein may perform a crucial cellular function in higher eukaryotes.     

Monitoring of early events of experimental woodchuck hepatitis infection: Studies of peripheral blood mononuclear cells by cytofluorometry and PCR

Abstract The peripheral blood mononuclear cells (PBMC) of woodchucks experimentally infected by woodchuck hepatitis virus (WHV) were examined simultaneously for the presence of membrane associated WHV antigens by cytofluorometry, and for WHV DNA and RNA sequences by the polymerase chain reaction (PCR). Four woodchucks were inoculated: two with a well-defined infectious inoculum and two with an inoculum obtained from an animal at the late incubation phase, which was positive for WHV DNA by PCR but still devoid of WHV markers. Infection was demonstrated in all four inoculated woodchucks by the appearance at different times of WHV DNA and WHV antigens in both leucocytes and serum. WHV DNA was first detected by PCR either in the serum (two cases) or in leucocytes (two cases). The mean percentage of cells positive for membrane associated WHsAg or WHcAg detected by cytofluorometry were 37%±25 and 17%±15 respectively. After 8 weeks, all inoculated animals were WHsAg positive in serum. These data suggest that PBMC are involved in the early events of hepadnavirus infection. They also show that sera which are positive by PCR for WHV DNA may transmit viral infection even while still seronegative for WHV markers and for WHV DNA by dot blot.     

Assignment of Listeria grayi and Listeria murrayi to a single species, Listeria grayi, with a revised description of Listeria grayi.

The genomic relatedness between Listeria grayi and Listeria murrayi was reevaluated by using DNA-DNA hybridization, multilocus enzyme electrophoresis, and rRNA restriction fragment length polymorphism techniques. The high levels of similarity observed between the strains of these two species confirmed the data published since 1973 and indicated that they should be considered members of a single species. On grounds of priority, the species should be named L. grayi.     

Site-directed mutants of human myeloperoxidase. A topological approach to the heme-binding site.

Two site-directed mutants of human promyeloperoxidase, MPO(His416----Ala) and MPO(His502----Ala), have been expressed in Chinese hamster ovary cells and purified. Overall purification yields and apparent molecular masses of the mutant proteins were similar to those of the wild-type enzyme. Both mutant species were analyzed spectroscopically to check the presence of the hemic iron in the proteins and were assayed for peroxidase activity. The data show that substitution of His502 leads to the loss, or to an inappropriate configuration, of the heme together with the loss of activity, suggesting that this residue could be the proximal His involved in the binding to the iron centers. On the other hand, substitution of His416 by alanine had no effect on either of the studied parameters.     

Spectral and enzymatic properties of human recombinant myeloperoxidase: comparison with the mature enzyme.

Human recombinant myeloperoxidase (recMPO), purified from an engineered Chinese hamster ovary (CHO) cell line, has been characterized and compared to the mature enzyme isolated from polymorphonuclear leukocytes. Both molecules appear essentially similar in physicochemical enzymatic terms according to the following observations. 1. The unprocessed recombinant protein displays the characteristic light absorption spectra of ferric mature MPO and exhibits its typical spectral changes in the presence of dithionite or hydrogen peroxide. 2. The addition of 14C-labeled 5-aminolevulinic acid, a heme precursor, to the culture medium of recombinant CHO cells yields labeled recMPO, indicating the presence of a heme-like structure in the molecule. 3. Like mature MPO, recMPO has a peroxidatic activity and catalyzes the oxidation of chloride ions in the presence of hydrogen peroxide, producing hypochlorous acid as measured by the monochlorodimedon assay. For both enzymes, the chlorinating activity optimally occurs around pH 5.0 at about 100 microM of hydrogen peroxide and is strongly inhibited by methimazole. 4. Diethylpyrocarbonate significantly reduces the enzymatic activity of both molecules, suggesting that histidine residues may be of prime importance in the active site of the enzymes. 5. According to infrared spectroscopy data, both enzymes present a very similar secondary structure organization. In conclusion, the data suggest that the processing of the precursor enzyme (recMPO) into the mature form occurs without major structural and functional consequences.