Salt-induced conformational transition of poly(d2NH2A-dT) studied by ultraviolet resonance Raman spectroscopy.

The conformational changes of poly(d2NH2A-dT) in aqueous solution, induced by increasing the NaCl concentration from 0.1M to 4M, have been monitored by ultraviolet resonance Raman spectroscopy, in using the 222-, 257- and 281 nm excitation wavelengths. These changes have been interpreted in comparing the polymer spectra to those of the mononucleotide compounds on one hand, and to those of other alternating purine-pyrimidine polymers on the other hand, i.e. poly(dG-dC) and poly(dA-dT) which showed a B to Z transition in going from low- to high salt concentrations. The high salt poly(d2NH2A-dT) spectra do not show any Raman marker line of the Z conformation. The spectroscopic results indicate that most of the ribose puckering goes from C2'-endo/anti to C3'-endo/anti in increasing the salt concentration. In addition the base stacking interactions, to which the resonance Raman effect is very sensitive, are not drastically changed upon salt variations. Thus the high salt structure of poly(d2NH2A-dT) remains a right-handed helix, likely under a dominant A conformation.     

Interaction between the Ricinus sanguineus agglutinin and receptor sites isolated from normal human lymphocytes.

Solubilized surface proteins from normal human lymphocytes were obtained by mild trypsin digestion. The binding of membrane components to labelled Ricinus sanguineus agglutinin (molecular weight = 120,000 daltons) was studied by a gel filtration method. The bound and unbound lectin amounts were determined from the gel filtration patterns. The binding parameters were calculated from Scatchard plots. They were compared to the parameters obtained at the same temperature for the lectin-intact lymphocyte system. The respective values for the affinity constant, were 3.5 x 10(6) M-1 and 6 x 10(6) M-1. The calculation of the number of sites per cell in each system specifies the yield of the trypsin digestion.     

On limiting nutrient patchiness and phytoplankton growth: a conceptual approach

A theoretical framework is developed to explore the effectsof limiting nutrient patchiness on phytoplankton growth. Growthrate is represented as a function of the average ambient substrateconcentration in the medium, the degree of patchiness and thepatch duration. Phytoplankton growth, in relation to the externalsubstrate concentration, is mediated by the cell quota for thelimiting nutrient. Two general conclusions can be drawn from this study. Firstthe degree of patchiness in the environment can affect individualgrowth rates and thus alter community structure even thoughthere is no change in the average ambient nutrient concentration.Second, for patch-adapted populations, the apparent K_s for growthcan be lowered significantly by making the distribution of thelimiting nutrient patchy with respect to time. The insightswhich this model provides into future experimental methodologiesare also discussed. ¹ Address for reprints ² also Dept. Botany ³ also Institute of Applied Mathematics     

Optimization of somatic cell injection in the perspective of nuclear transfer in goldfish

Background  

Nuclear transfer has the potential to become one strategy for fish genetic resources management, by allowing fish reconstruction from cryopreserved somatic cells. Survival rates after nuclear transfer are still low however. The part played by unsuitable handling conditions is often questioned, but the different steps in the procedure are difficult to address separately. In this work led on goldfish (Carassius auratus), the step of somatic cells injection was explored. Non-enucleated metaphase II oocytes were used as a template to explore the toxicity of the injection medium, to estimate the best location where the cell should be injected, and to assess the delay necessary between cell injection and oocyte activation.     

Poly(dA-dT) complexes with histone H1 and pancreatic ribonuclease: Specific base recognition evidenced by ultraviolet resonance Raman spectroscopy

The conformational changes of poly(dA-dT) from random coil to ordered structure with stacked bases produce important changes in the Raman line intensities (hypochromism) when the polymer is excited under the preresonance Raman conditions (λ excitation = 300 nm). Poly(dA-dT)–RNase and poly(dA-dT)–histone H1 interactions have been studied as models of mechanisms of destabilization and stabilization by proteins of the DNA secondary structure, respectively, following this intense preresonance Raman hypochromism. In addition, the specific variation of the intensity of the 1582-cm^?1 line of adenine is interpreted in terms of the interaction of the amino group with the RNase (thus involving the large groove). In the poly(dA-dT)–H1 complex, the intensity of the 1665-cm^?1 line of thymine increases. This increase appears to involve the C₂?O group of thymine, located in the narrow groove.     

Alginate-entrapped Haslea ostrearia as inoculum for the greening of oysters

Entrapment in calcium alginate beads of the marine diatom, Haslea ostrearia, was successfully used for stock-culture managment and afterwards the sowing of ponds for the greening of oysters. After storage during almost 2 months, viable and cultivable cells were recovered from beads by dissolving alginate matrix but an original way lies in directly introducing beads in ponds and promoting natural cell leakage. © Rapid Science Ltd. 1998