Showing papers by "Bulgarian Academy of Sciences published in 1981"

The structure of the yeast ribosomal RNA genes. 4. Complete sequence of the 25 S rRNA gene from Saccharomyces cerevisiae

Abstract: The complete nucleotide sequence of the 25 S rRNA gene from one rDNA repeating unit of Saccharomyces cerevisiae has been determined The corresponding 25 S rRNA molecule contains 3392 nucleotides and has an estimated relative molecular mass (Mr, Na-salt) or 117 x 10(6) Striking sequence homology is observed with known 5'- and 3'-end terminal segments of L-rRNA from other eukaryotes Possible models of interaction with 58 S rRNA are discussed

Common black and Newton film formation

Abstract: By model investigations of microscopic foam films (stabilized with sodium octyl sulfate, NaOS, and sodium dodecyl sulfate, NaDoS, in the presence of electrolyte) and by study of the properties of the adsorbed layers of the solutions it is shown that the adsorbed layers at the interface are essential for the formation of common black and Newton black spots and films. The adsorption isotherms are obtained using a precise spherotensiometric method. The model microscopic film with a radius of 10−2 cm that has been used makes it possible to work at very low surfactant concentrations and thus the lowest surfactant concentration at which a black spot appears has been found. The concentrations of formation of common black spots and Newton black spots are distinguished. A correlation between the probability of the formation of black spots (common and Newton) and the state of the adsorbed layer is established. For instance, the formation of common black spots and the deviation from the ideal state in the adsorbed layer are related to the formation of associates (premicelles) in the bulk and their adsorption at the interface. The formation of common black spots with a probability of one occurs at a concentration close to the saturation concentration Γ∞ of the adsorbed substance. The close packing of the molecules at the interface is a necessary condition for the formation of Newton black spots. The formation of Newton black spots with a probability of one occurs at a somewhat higher concentration (two to three times higher than the concentration corresponding to the closest packing of molecules at the interface). The dependence of the lifetime (stability) of the two types of black films (common and Newton) on the surfactant concentration is also studied. It is found that at a definite concentration (different for the common black and Newton films) the film persistence increases steeply. It is shown that the proposed surface model is not decisive for the understanding of this stability (unlike the formation of the two types of black films).

Photochromism and dynamic holographic recording in a rigid solution of fluorescein

Abstract: An investigation was made of the spectra, the kinetics of induction and thermal decay and the dichroism of the photoinduced triplet absorption band in a rigid solution of fluorescein in orthoboric acid. Dynamic holographic recording was possible on this material. An experimental study was conducted into the polarizing properties of the volume transmission holograms. The experiments on four-wave mixing with continous laser light revealed a very high resolution for this rigid solution when used as a medium for optical recording. As a result of the investigations, some possible applications of the rigid solution of fluorescein are pointed out.

The structure of the yeast ribosomal RNA genes. 3. Precise mapping of the 18 S and 25 S rRNA genes and structure of the adjacent regions

Abstract: The 5'-terminal of Saccharomyces cerevisiae 18 S and 25 S rRNA are precisely mapped within the sequence of the rDNA repeating unit. The 3'-terminal of 25 S rRNA and 37 S pre-rRNA are located within a 548 bp segment of the rDNA repeating unit by the use of a DNA polymerase I extension technique. The analysis of the rDNA sequences at the structural gene boundaries reveals the presence of oligonucleotide repeats which may be involved in transcription or processing control mechanisms. The sequence of rDNA in the transcription termination region is determined and possible mechanisms shaping the 3'-end of 25 S rRNA are discussed.

Water condensation on hexadecane and linear tension

Abstract: A new method has been developed for the investigation of the condensation from supersaturated vapor on substrates by the adiabatic compression of a saturated vapor gas. The condensation was detected by light scattering, measured with a photomultiplier. A maximum critical supersaturation of about 42% at room temperature (t = 20°C) was found for water condensation on hexadecane. This value was shown to be 2.5 times less than the value to be expected according to the prevailing interpretation of heterogeneous phase formation, following Volmer's pattern. But, when taking into account the linear tension of the nucleus lens perimeter, good agreement was obtained with the critical supersaturation found at a linear tension of about −0.8 × 10−5 dyne. Equations for the work of formation of a liquid nucleus on a liquid substrate, deduced in the paper, underlie the discussion.

The Primary Passive Film on Li in SOCl2 Electrolyte Solutions

Abstract: The primary passive film on Li in electrolyte solutions is studied by galvanostatic pulse technique. The evolution of the resistance and capacitance of the Li electrode in solutions of under open‐circuit conditions is interpreted in terms of a two‐stage process involving the formation of a continuous dense film and its growth by ion migration and/or diffusion across the solid film. The film resistivity, its activation energy, the Tafel current‐field relation, and the high field transients give evidence for an ion conducting solid film. The film growth is limited by its chemical dissolution. The rate of the latter controls the self‐discharge rate of the Li anode as well as the growth of the secondary porous film, which is responsible for the voltage delay effects in primary cells.

Formation of holographic diffraction gratings in photoresist

Abstract: The exposure-development process for the fabrication of holographic diffraction gratings for integrated optics in the positive photoresist Shipley AZ-1350 is theoretically and experimentally investigated. An analysis of the light intensity distribution is carried out, taking into account the reflectivity at the photoresist-substrate interface and the attenuation in the photoresist for two holographic exposure arrangements. The influence of the exposure energy, the development time for a fixed concentration of the developer and the initial photoresist thickness are described. Various grating profiles are calculated for photoresist films, coated on matched and reflective substrates. Scanning electron micrographs demonstrate very good agreement between the actual and calculated gratings profiles.

A simple charge‐based DLTS technique

Abstract: A charge-based DLTS technique is proposed for characterizing the interface states and, with some restrictions, the bulk traps in MIS, p–n, and Schottky-barrier diodes. The technique uses very simple devices — a mechanical chopper and a standard electrometer, but inspite of this a high sensitivity of the order of 108 eV−1 cm−2 can be reached when interface density is measured. The charge-based technique is more suitable than the capacitive one, when MIS capacitors made on high resistivity semiconductor material or such with a very thin insulating layer are studied. Es wird eine Ladungs-DLTS-Technik zur Charakterisierung der Grenzflachenzustandsdichte und mit einigen Einschrankungen auch der Volumenterme in MIS-, p–n- und Schottky-Dioden beschrieben. Die Technik benutzt sehr einfache Gerate — einen Zerhacker und ein Standardelektrometer. Trotzdem besitzt sie jedoch eine hohe Empfindlichkeit (108 eV−1 cm−2) fur die Grenzflachenzustandsdichte. Die Ladungs-DLTS-Technik hat gewisse Vorteile vor der kapazitiven DLTS Technik, wenn MIS-Strukturen mit hochohmigen Halbleitersubstraten oder mit sehr dunnen Isolatorschichten untersucht werden.

Edge energy and pore stability in bilayer lipid membranes

Abstract: The problem of pore formation in two-dimensional liquid crystal systems like lipid bilayers, biomembranes and black foam films is considered in terms of a unified molecular structure of the pore, using as a basic parameter the edge energy γ per unit length of the pore perimeter.

Associative interactions and surface tension in ionic surfactant solutions at concentrations much lower than the cmc

Abstract: The surface pressure isotherms Δσ(CS) of the ionic surfactants sodium dodecyl sulfate (NaDOS) and sodium octyl sulfate (NaOS) were measured using at different electrolyte concentration an accurate and sensitive sphere tensiometer. At 10−1 mole/liter NaCl, two particular points on the isotherms were noticed for surfactant concentrations below 10−4 mole/liter. The first, at Δσ ≈ 0.5 dyn/cm, corresponds to the formation of flat premicelles in the solution, whereas the second corresponds to a phase transition in the adsorbed layer and this is probably associated with the disintegration of the premicelles on the surface but not in the bulk of the solution. The supplementary measurements of the surface potential and the time dependence of the surface tension show evidence of this hypothesis.

Formation of hybrid nucleosomes containing new and old histones

Abstract: 5 mM hydroxyurea (HU) inhibits DNA synthesis in mouse P815 cells by 94-97% in less than 1 hr. Nevertheless, histone synthesis continues and newly-synthesised histones are incorporated into non-replicating chromatin at a rate of about 20% of that in control exponentially-growing cells. To study the organization of these histones in chromatin P815 cells were treated with 5 mM HU in medium containing dense (15N, 13C, 2H) - substituted amino acids. After inhibition of DNA synthesis, newly-synthesised histones were labelled with (3H)-arginine. The cells were harvested 90 min later, and mono- and oligonucleosomes were prepared and analysed on metrizamide-triethanolamine (MA-TEA density gradients. Analysis of the distribution of 3H-labelled histones in these gradients shows that they are incorporated into hybrid mononucleosomes containing both new and old histones. It is also shown that these hybrid nucleosomes are not randomly distributed, but show a certain tendency to be clustered in certain chromatin regions.

On the inelastic-loss approximation for keV-energy ion collisions in solids

Abstract: Inelastic energy-loss in a single collisionT e and related stopping cross-sectionT e based on the Firsov model are evaluated for different screening functions in the elastic interaction potentials. Various approximations ofT e andS e for keV-ions in solids are discussed.