Vertical distribution of zooplankton in the frontal zone of the Gulf Stream and Labrador Current

Zooplankton data collected during September 1995 in the NorthWest Atlantic at 4139'N, 4958'W (the location of the siteof the ‘Titanic’ wreck) were analysed. The regioninvestigated was characterized by a very sharp frontal zonebetween the Gulf Stream and the main stream of the LabradorCurrent. The total plankton biomass in the water column wasvery high. The macroplankton biomass values below the 600 mlayer were significantly higher as compared with the similarvalues measured before in other productive boreal regions ofthe Atlantic and Pacific oceans. A lot of dead mesoplanktonanimals occurred in the deep layers. The reason was that thecold-water mesoplankton advected by the Labrador Current diedoff intensively within the deep layers of the frontal zone andwere used as a food resource by the macroplankton carnivoresand scavengers that were very abundant there.     

Hydroxyurea treatment does not prevent initiation of DNA synthesis in Ehrlich ascites tumour cells and leads to the accumulation of short DNA fragments containing the replication origins

The ability of EAT cells to initiate DNA synthesis in the presence of high doses of hydroxyurea was examined using the recently developed method for crosslinking DNA in vivo. Since crosslinking blocks elongation but has little effect on initiation (Russev and Vassilev (1982) J. Mol. Biol. 161, 77-87), this approach permits a separate study of the two stages of the DNA replication. We found out that hydroxyurea did not greatly affect the initiation of DNA replication but strongly inhibited the elongation of the already initiated new DNA chains. This resulted in the formation of short fragments enriched in sequences synthesized at and around the sites where DNA initiation began. These fragments were not ligated to the high molecular weight chromosomal DNA and could be released under denaturing conditions in single-stranded form. The reassociation and electrophoretic analysis showed that they contained about 200 nucleotides long interspersed DNA sequences repeated approx. 10(4) times per haploid genome, that probably served as replication origins.     

The cationic polymerization of 3-O-acetyl-β-arabinofuranose 1,2,5-orthobenzoate

Cationic polymerisation of 3-O-acetyl-β-L-arabinofuranose 1,2,5-orthobenzoate initiated by either triphenylcarbonium tetrafluoroborate or benzoylium perchlorate has been studied. The existence of living chains was demonstrated by termination of polymerisation with tritium-labelled 1-butanol. The number of growing chains reached a maximum after ≈10 min and then decreased.     

Mapping an origin of DNA replication at a single-copy locus in exponentially proliferating mammalian cells.

A general method for determining the physical location of an origin of bidirectional DNA replication has been developed recently and shown to be capable of correctly identifying the simian virus 40 origin of replication (L. Vassilev and E. M. Johnson, Nucleic Acids Res. 17:7693-7705, 1989). The advantage of this method over others previously reported is that it avoids the use of metabolic inhibitors, the requirement for cell synchronization, and the need for multiple copies of the origin sequence. Application of this method to exponentially growing Chinese hamster ovary cells containing the nonamplified, single-copy dihydrofolate reductase gene locus revealed that DNA replication begins bidirectionally in an initiation zone approximately 2.5 kilobases long centered about 17 kilobases downstream of the DHFR gene, coinciding with previously described early replicating sequences. These results demonstrate the utility of this mapping protocol for identifying cellular origins of replication and suggest that the same cellular origin is used in both the normal and the amplified DHFR locus.     

Emetine allows identification of origins of mammalian DNA replication by imbalanced DNA synthesis, not through conservative nucleosome segregation.

In the presence of emetine, an inhibitor of protein synthesis, nascent DNA on forward arms of replication forks in hamster cell lines containing either single or amplified copies of the DHFR gene region was enriched 5- to 7-fold over nascent DNA on retrograde arms. This forward arm bias was observed on both sides of the specific origin of bidirectional DNA replication located 17 kb downstream of the hamster DHFR gene (OBR-1), consistent with at least 85% of replication forks within this region emanating from OBR-1. However, the replication fork asymmetry induced by emetine does not result from conservative nucleosome segregation, as previously believed, but from preferentially inhibiting Okazaki fragment synthesis on retrograde arms of forks to produce 'imbalanced DNA synthesis'. Three lines of evidence support this conclusion. First, the bias existed in long nascent DNA strands prior to nuclease digestion of non-nucleosomal DNA. Second, the fraction of RNA-primed Okazaki fragments was rapidly diminished. Third, electron microscopic analysis of SV40 DNA replicating in the presence of emetine revealed forks with single-stranded DNA on one arm, and nucleosomes randomly distributed to both arms. Thus, as with cycloheximide, nucleosome segregation in the presence of emetine was distributive.     

Dependence of 13C chemical shifts on the spatial interaction of protons,and its application in structural and conformational studies of oligo- and poly-saccharides

Regularities in the variation of chemical shifts and the glycosidation effects in the ¹³C-n.m.r. spectra of disaccharides were found to depend on the configuration at the anomeric centre of the glycosidating pyranose, and the absolute configuration of both pyranoses moieties. These empirical regularities are explained in terms of the spatial proton-proton interactions within the statistically averaged, or preferred, conformation near the glycosidic linkage. The applicability of these effects for the determination of the anomeric and absolute configuration and the sequence of pyranose residues in oligo- and poly-saccharides is discussed. The conformational properties of glycosidic linkages in disaccharides and disaccharide fragments of oligo- and poly-saccharides are compared on the basis of ¹³C-n.m.r. data.     

The in vitro screening of methylated 4-oxypiperidine compounds for inhibition of protein synthesis in a rabbit reticulocyte cell-free translation system

A variety of methylated 4-oxypiperidine derivatives were tested for their ability to inhibit protein synthesis in vitro. A direct correlation was found between the extent of methylation of these compounds and their inhibitory activity in a rabbit reticulocyte lysate cell-free translation system.Abbreviation IC₅₀ 50% inhibitory concentration     

Life-cycle,delimitation and redescription of Catatropis verrucosa (Frölich, 1789) Odhner, 1905 (Trematoda: Notocotylidae)

The life-cycle of Catatropis verrucosa (Frölich, 1789) Odhner, 1905 has been completed experimentally starting from infected snails collected along the River Danube in Europe. Each stage of the life-cycle is redescribed. Taxonomic problems are discussed and the main features of the species are listed. Synonyms for C. verrucosa are Fasciola verrucosa Frölich, 1789, F. anseris Gmelin, 1790, Monostoma verrucosa (Frölich, 1789) Zeder, 1800, and Catatropis charadrii Skrjabin, 1915. Other names, such as Notocotylus triserialis Diesing, 1839, Notocotyle triseriale (Diesing, 1839) Diesing, 1850, Monostoma verrugueux Dujardin, 1845, “Monostoma sp. du canard” of Blanchard (1847), Notocotyle verrucosum (Frölich, 1789) Monticelli, 1892, N. verruqueux Railliet, 1895, and Distoma verrucosum (Frölich, 1789) Wolffhugel, 1900, were found to represent adults and/or larvae of C. verrucosa. Conversely, but less often, adults and larvae of other species were found described and illustrated as C. verrucosa. One of these, C. verrucosa of Joyeux (1922), was renamed Pseudocatatropis joyeuxi Kanev & Vassilev, 1986. Occasionally, authors actually working with C. verrucosa ascribed their results to different species. Based on experimental life-cycle studies, the following facts were demonstrated. (1) The first intermediate hosts are the prosobranch freshwater snails Bithynia tentaculata (Linnaeus, 1758) and B. leachi (Leach, 1818). (2) The same snails are also first intermediate hosts for Notocotylus imbricatus (Looss, 1893) Szidat, 1935, N. parviovatus Yamaguti, 1934, and N. ponticus Tschiaberaschvili, 1966. In all these species, the species characteristics are expressed by the adult morphology only, and the larvae cannot be identified by morphological criteria. It is proposed that tri-oculate monostome cercariae found in naturally infected B. tentaculata and B. leachi be referred to as “Cercaria imbricata group”. These cercariae include Cercaria imbricata Looss, 1893, C. helvetica I Dubois, 1928, C. triophthalmia Faust, 1930, C. fennica I Wikgren, 1956; C. ephemera of Lutta (1934); C. monostomi of Mathias (1925), Lutta (1934) and Zdun (1961), Cercaria Notocotylus attenuatus of Francalanci & Manfredini (1969), and Monostome cercaria I Emmel, 1943. (3) There is no second intermediate snail host in the life-cycle of C. verrucosa. (4) The final hosts are birds. (5) The adult worms possess, on the ventral body surface, a median ridge and two lateral rows of 12 (range 11–14) papillae per row.