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 thiol proteinases from the latex of Carica papaya L. III. The primary structure of chymopapain

The amino-acid sequence of chymopapain is presented. It was isolated from the latex of the fruits from the tropical species Carica papaya L. and is, besides papain and papaya proteinase omega, the third thiol proteinase from this source. The primary structure contains 218 amino-acid residues. It was deduced from sequence analysis of the native enzyme and of peptides obtained by tryptic, chymotryptic, peptic, thermolysinolytic and mild acidic hydrolysis. Out of a total of eight cysteine residues, six are involved in the formation of three disulfide bonds, the location of which has been established with the help of peptic and thermolysinolytic peptides and fragments, obtained by mild acidic hydrolysis. Chymopapain shares 126 identical amino-acid residues (58%) with papain and 141 (65%) with papaya proteinase omega, including the three disulfide bridges and the free cysteine in position 25, required for activity. Except some amino-acid residues in the substrate-binding site, all residues involved in the catalytic mechanism are conserved. The homology between papaya proteinases is discussed.     

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, + +.     

Compositional heterogeneity of the Escherichia coli genome: A role for VSP repair?

E. coli genes that contain a high frequency of the tetranucleotide CTAG are also rich in the tetramers CTTG, CCTA, CCAA, TTGG, TAGG, and CAAG (group-I tetramers). Conversely, E. coli genes lacking CTAG are rich in the tetranucleotides CCTG, CCAG, CTGG, and CAGG (group-II tetramers). These two gene samples differ also in codon usage, amino acid composition, frequency of Dcm sites, and contrast vocabularies. Group-I tetramers have in common that they are depleted by very-short-patch repair (VSP), while group-II tetramers are favored by VSP activity. The VSP system repairs G:T mismatches to G:C, thereby increasing the overall G+C content of the genome; for this reason the CTAG-rich sample has a lower G+C content than the CTAG-poor sample. This compositional heterogeneity can be tentatively explained by a low level of VSP activity on the CTAG-rich sample. A negative correlation is found between the frequency of group-I tetramers and the level of gene expression, as measured by the Codon Adaptation Index (CAI). A possible link between the rate of VSP activity and the level of gene expression is considered.Correspondence to: A. Marine     

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.     

再论假裸枝叠层石科*

内蒙古桌子山地区中奥陶统公乌素组遗迹化石十分丰富.本文共鉴定、描述14个遗迹属、17个遗迹种,其中1新遗迹属——Biscopulatichnus、4新遗种和6未定种.并根据不同遗迹属在不同层位中的相对丰度,建立了4个遗迹组合,自下而上的顺序是:1. Taenidium-Phycodes 组合;2. Volkichnium 组合;3. Helminthopsis 组合;4. Granularia-Circulichnus 组合,大致相当于 Seilacher (1967) 的 Zoophycos 遗迹相,反映出公乌素组沉积期,水体较深且宁静、缺氧、有机质含量高,推测应为大陆斜坡环境.     

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.