The use of photosynthesis inhibitor (DCMU) for in situ metabolic and primary production studies on soft bottom benthos

A selective chemical photosynthesis inhibitor, DCMU (Dichorophenyl-dimethylurea), dissolved in DMSO (Dimethyl sulfoxide) was substituted for the dark incubation method commonly used to measure the oxygen consumption in metabolic and primary production studies. We compared oxygen fluxes during light incubations with DCMU and dark incubations procedure, on soft bottom benthos. For this purpose, we studied the effects of different DCMU concentrations. A concentration of 5 · 10^–5 mol l^–1 inside a clear incubation enclosure completely inhibits photosynthesis without affecting the metabolism of soft bottom benthos.     

Isolation and phenotypic analysis of conditional-lethal, linker-insertion mutations in the gene encoding the largest subunit of RNA polymerase II in Saccharomyces cerevisme

Summary Linker-insertion mutagenesis was used to isolate mutations in the Saccharomyces cerevisiae gene encoding the largest subunit of RNA polymerase II (RP021, also called RPBI). The mutant rpo21 alleles carried on a plamid were introduced into a haploid yeast strain that conditionally expresses RP021 from the inducible promoter pGAL10. Growth of this strain on medium containing glucose is sustained only if the plasmid-borne rpo21 allele encodes a functional protein. Of nineteen linker-insertion alleles tested, five (rpo21-4 to –8) were found that impose a temperature-sensitive (ts) lethal phenotype on yeast cells. Four of these five is alleles encode mutant proteins in which the site of insertion lies near one of the regions of the largest subunit that have been conserved during evolution. Two of the is mutants (rpo21-4 and rpo21-7) display pleiotropic phenotypes, including an auxotrophy for inositol and a decreased proliferation rate at the permissive temperature. The functional relationship between RP021 and RP026, the gene encoding the 17.9 kDa subunit shared by RNA polymerases 1, 11, and III was investigated by determining the ability of increased dosage of RP026 to suppress the is phenotype imposed by rpo21-4 to –8. Suppression of the is defect was specific for the rpo21-4 allele and was accompanied by co-suppression of the inositol auxotrophy. These results suggest that mutations in the largest subunit of RNA polymerase II can have profound effects on the expression of specific subsets of genes, such as those involved in the metabolism of inositol. In the rpo21-4 mutant, these pleiotropic phenotypes can be attributed to a defective interaction between the largest subunit and the RP026 subunit of RNA polymerase II.     

Biomass and composition of size fractionated phytoplankton in the Weddell-Scotia Confluence area

Summary The measurement of Chl a, Chl b and Chl c contents in four size fractions (Nuclepore filters of 10 m, 3m, 1 m and 0.2 m pore-size) together with microscopic examination illustrate the structure and the relative importance of the micro-, nano and pico-phytoplankton in the production system in the Weddell/Scotia Confluence area. In the Scotia Sea, large diatoms were prevalent and their biomass increased during the six week cruise period, exceeding 1 mg Chl a m^–3 at the beginning of January. In contrast, in the Marginal Ice Zone of the Weddell Sea, the biomass remained low, up to 0.3 mg Chl a m^–3. A diversified nanoplankton community accounted for more than 90% of this biomass: small diatoms, naked dinoflagellates, cryptophyceans, prymnesiophytes and green flagellates which increased the Chl b/Chl a ratio to values >0.20. An important trend affected the Confluence area, where a high biomass net-plankton community (4 mg Chl a m^–3) rapidly changed towards a uniform nanoplankton system of the same kind as in the Weddell Sea. At times, autotrophic cryptophyceans were almost dominating (>4.10⁶ cells/l), with a biomass up to 2 mg Chl a m^–3 and a low phaeopytin ratio (<10%). This situation probably arises because of a grazing pressure by krill. However, due to the geographic and oceanographic peculiarities of this area, it is not possible to extrapolate these observations concerning the size structure of the primary producers to the Southern Ocean in general.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Basic nuclear proteins of the histone-less eukaryote Crypthecodinium cohnii (Pyrrhophyta): two-dimensional electrophoresis and DNA-binding properties

Unlike typical eukaryotes, the Dinoflagellate Crypthecodinium cohnii does not contain histones but six major basic, low molecular weight nuclear proteins which represent only 10% of the DNA mass and differ from histones in their electrophoretic and DNA-binding properties. These proteins are resolved in two-dimensional electrophoresis (AUT-PAGE x SDS-PAGE). Three proteins with an apparent molecular mass of 16, 16.5 and 17 kDa (p16, p16.5 and p17) are present in addition to the major 14 kDa basic nuclear component (HCc). HCc itself is resolved in three proteins (alpha, beta and gamma). When the proteins are not reduced with 2-mercaptoethanol before 2D-PAGE, the migration of HCc alpha, beta and gamma is modified in a way which suggests the formation of both inter- and intramolecular disulfide bridges and thus, the presence of at least two cysteines. The amino-acid analysis of HCc proteins resolved in 2D gels confirms that they are lysine-rich. HCc alpha, beta and gamma as well as p16, p16.5 and p17 are removed from isolated chromatin with 0.6 M NaCl, indicating that their affinity for DNA in vivo is lower than that of core histones. Furthermore, in vitro, they bind more tightly to single-stranded than to double-stranded DNA.     

Glucocorticoid hormones increase the activity of γ-glutamyltransferase in a highly differentiated hepatoma cell line

γ-Glutamyltransferase activity was detected in the plasma membrane of the highly differentiated hepatoma cell line Fao, (0.93 mU/mg cell protein). Dexamethasone (1 μM) provoked a 2–3-fold increase in the activity of the enzyme in the presence of fetal calf serum. Maximal induction occurred 48–72 h after addition of the glucocorticoid to the cell culture medium. The hormonal specificity was demonstrated by the relative potencies of several glucocorticoids and sex steroids: hydrocortisone and corticosterone increased γ-glutamyltransferase activity while tetrahydrocorticosterone and all sex steroids tested were ineffective. The effect of dexamethasone on γ-glutamyltransferase activity was specific since the activities of several other plasma membrane enzymes were not modified. The mechanism of the dexamethasone-induced increase in γ-glutamyltransferase activity was neither by modification of the affinity of the enzyme for its substrates nor by alteration of the subcellular distribution of the enzyme. This increase was prevented by cycloheximide and actinomycin D. The data presented are consistent with a specific glucocorticoid receptor-mediated induction of γ-glutamyltransferase activity in Fao cells. The kinetic parameters of the induction process by glucocorticoids are very similar to those found in adult rat liver. These results suggest that the Fao cell line is a very convenient system for the study of the molecular mechanisms of glucocorticoid effects on differentiated cells.     

Modifications of ganglioside composition in peripheral nerve of myelin deficient trembler mutant mouse

Ganglioside distribution was studied in peripheral nerves of normal controls and those of Trembler mutant mouse with defect in Schwann cell differentiation and myelination. Neuraminic acid content was considerably decreased in the mutant. Ganglioside distribution as evaluated by densitometry of resorcinol positive spots on thin-layer chromatography revealed a major peak for GDl_a in normal controls. In the mutant, the relative proportion was modified with qualitative modifications in the GDl_a area and a tremendous increase in GM₃ content. The relation with the intense Schwann cell proliferation observed in the mutant is discussed.     

IF-3 crosslinking to Escherichia coli ribosomal 30 S subunits by three different light-dependent procedures: Identification of 30 S proteins crosslinked to IF-3—Utilization of a new two-stage crosslinking reagent, p-nitrobenzylmaleimide

We here report the results of using three light-dependent procedures for crosslinking IF-3 to 30 S proteins within an IF-3·30 S complex. In the first procedure, employing FMN as a photosensitizer, protein S12 is found to be the only major crosslinked protein. In the second procedure, IF-3 is first reacted with the new two-stage crosslinking reagent, p-nitrobenzylmaleimide (PNBM), and the PNBM—IF-3·30 S complex is irradiated. The major crosslinked proteins are S3 > S2, S12, S18. Small amounts of crosslinked S11 and S21 are also found. In the third procedure, the IF-3·30 S complex is reacted with PNBM and then irradiated. The major crosslinked proteins are S12 > S3 > S11 and small amounts of crosslinked S1, S13, and S21 are also found. These results are compared with results obtained by others using different crosslinking procedures and are used to discuss the Lake and Kahan model (J. A. Lake and L. Kahan, 1975, J. Mol. Biol., 99, 631–644, and J. A. Lake, 1978, in Advanced Techniques in Biological Electron Microscopy II, Koehler, J. K., ed., pp. 173–211, Springer-Verlag, Berlin) for IF-3 binding to 30 S subunits.     

Effect of angiotensin II and norepinephrine on release of prostaglandins E2 and I2 by the perfused rat mesenteric artery

Prostaglandin E₂ (PGE₂) and 6 keto-PGF_1α, the stable metabolite of prostacyclin (PGI₂), have been measured in the effluent of perfused rat mesenteric arteries by the use of a sensitive and specific radioimmunoadday (RIA) method. The PGE₂ and 6-keto-PGF_1α were continuousyl released by the unstimulated mesenteric artery over a period of 145 min. After 100 min of perfusion the release of PGE₂ and 6-keto-PGF_1α was 4.5 ± 8.4 pg/min and 254 ± 75 pg.min respectively, which is in accord with the general belief that PGI₂ is the major PG synthesized by arterial tissue. Angiotensin II (AII) 5 ng/ml) induced an increased of PGE₂ and 6-keto-PGF_1α release without changing the perfusion pressure. The effect of norepinephrine (NE) injections on release of PGs depended on the duration of the stabilization period. The changes of perfusion pressure induced by NE were not related to changes in release of PGs. Thus, it seems that the increase of PG release induced by AII and NE was due to a direct effect of the drugs on the vascular wall. This may represent an important modulating mechanism in the regulation of vascular tone.     

ZINC ADSORPTION AND TRANSPORT BY CHLAMYDOMONAS VARUIABILIS AND SCENEDESMUS SUBSPICATUS (CHLOROPHYCEAE) GROWN IN SEMICONTINUOUS CULTURE1

The amount of zinc adsorbed onto the cell surface of the unicellular green algae Scenedesmus subspicatus Hodat and Chlamydomonas variabilis Dangeard was operationally defined by extraction with EDTA; it was a function of the concentration of free ionic zinc remaining in the growth medium, rather than that of the total (free plus complexed) zinc concentration, and could be described by Langmuir isotherms. Conditional adsorption equilibrium constants for zinc were 0.123 and 0.039 L ·μmol^?1 for S. subspicatus and C. variabilis, respectively. A portion of the zinc adsorbed onto C. variabilis was released into solution after 1 h of contact with the metal, providing a possible tolerance mechanism for this alga; the division rate of C. variabilis was not altered by up to 12 μmol Zn²⁺· L^?1, although the cell yield obtained during the stationary phase was significantly decreased. The amount of transported or cellular zinc, for both algal species, was operationally defined as the zinc remaining with the cell after EDTA-extraction; it was a linear function of the free ionic zinc concentration remaining in solution, suggesting that the zinc transported into the cell was not derived from the total adsorbed fraction, although the latter may contain some zinc originating from specific sites leading to zinc transport.