Denaturation of β-sheet structure

A two-dimensional Ising model is used to study the thermal denaturation of parallel β-sheet structures in biomolecules.The fraction of intact hydrogen bonds and the excess heat capacity are evaluated as a function of the temperature.     

Viability of Homozygous Deficiencies in Somatic Cells of DROSOPHILA MELANOGASTER

The viability of cells made homozygous for different deficiencies by induced mitotic recombination was examined. The deficiencies varied in length from two to 30 polytene chromosome bands and were distributed over the five major chromosome arms. Among a sample of 30, ten deficiencies were cell viable. Our results show that 12% of the genome is necessary for cell survival, supporting previous estimates of about 5,000 genes in the genome of Drosophila.     

The effect of 2-oxoglutarate and biotin in the release of amino acids by Citrobacter intermedius C3

Excretion of amino acids by Citrobacter intermedius C3 was assayed in a mineral medium with glucose as carbon source. Glutamic acid is the main amino acid excreted in liquid medium and it is also detected at the colonial level in solid medium. Mutants with different behaviour with respect to the excretion of amino acids are studied. The presence of 2-oxoglutarate in the medium induced excretion in all strains. On the other hand when biotin was added to the culture media amino acid excretion was partially reduced.     

Behavior of Somatic Cells Homozygous for Zygotic Lethals in DROSOPHILA MELANOGASTER

The behavior in genetic mosaics of 86 EMS-induced sex-linked lethals has been studied. Seventy-five percent of them are autonomous in gynandromorphs. Forty-three lethals nonviable in sex mosaics have been analyzed in X-ray-induced spots in the abdominal tergites and the imaginal wing derivatives. Of the lethals, 90.7% are homozygous viable in mosaic spots, and only 9.3% have been classified as epidermal cell lethal. Thus, the fraction of the Drosophila genome essential for cell viability has been estimated to be about 420 genes. The phenotypes at the cellular level of some cell-viable mutations altering cell parameters (mitotic orientation, differentiation, etc.) are described.     

Role of motilin in the control of intestinal absorption, and gastric and biliary secretions in the rat

The effects of motilin on proline absorption and gastric and biliary secretions were examined in the rat. Prolonged intravenous administration of motilin (50 pmol/kg/min) significantly inhibited (P < 0.05) proline transport across the jejunum and reduced basal acid secretion to 40% of control value. The same concentration of motilin induced choleresis and increased bile output by 32%. Incubation of intestinal strips with different concentrations of motilin produced a dose-dependent inhibitory pattern of proline accumulation in the intestinal cells.     

A tomato endo-beta-1,4-glucanase, SlCel9C1, represents a distinct subclass with a new family of carbohydrate binding modules (CBM49)

A critical structural feature of many microbial endo-beta-1,4-glucanases (EGases, or cellulases) is a carbohydrate binding module (CBM), which is required for effective crystalline cellulose degradation. However, CBMs are absent from plant EGases that have been biochemically characterized to date, and accordingly, plant EGases are not generally thought to have the capacity to degrade crystalline cellulose. We report the biochemical characterization of a tomato EGase, Solanum lycopersicum Cel8 (SlCel9C1), with a distinct C-terminal noncatalytic module that represents a previously uncharacterized family of CBMs. In vitro binding studies demonstrated that this module indeed binds to crystalline cellulose and can similarly bind as part of a recombinant chimeric fusion protein containing an EGase catalytic domain from the bacterium Thermobifida fusca. Site-directed mutagenesis studies show that tryptophans 559 and 573 play a role in crystalline cellulose binding. The SlCel9C1 CBM, which represents a new CBM family (CBM49), is a defining feature of a new structural subclass (Class C) of plant EGases, with members present throughout the plant kingdom. In addition, the SlCel9C1 catalytic domain was shown to hydrolyze artificial cellulosic polymers, cellulose oligosaccharides, and a variety of plant cell wall polysaccharides.     

Infectivity determinants of the hepatitis B virus pre-S domain are confined to the N-terminal 75 amino acid residues

The N-terminal pre-S domain of the large hepatitis B virus (HBV) envelope protein plays a pivotal role at the initial step of the viral entry pathway. In the present study, the entire pre-S domain was mapped for infectivity determinants, following a reverse-genetics approach and using in vitro infection assays with hepatitis delta virus (HDV) or HBV particles. The results demonstrate that lesions created within the N-terminal 75 amino acids of the pre-S region abrogate infectivity, whereas mutations between amino acids 76 and 113, overlapping the matrix domain, had no effect. In contrast to the results of a recent study (L. Stoeckl, A. Funk, A. Kopitzki, B. Brandenburg, S. Oess, H. Will, H. Sirma, and E. Hildt, Proc. Natl. Acad. Sci. 103:6730-6734, 2006), the deletion of a cell membrane translocation motif (TLM) located between amino acids 148 and 161 at the C terminus of pre-S2 did not interfere with the infectivity of the resulting HDV or HBV mutants. Furthermore, a series of large deletions overlapping the pre-S2 domain were compatible with infectivity, although the efficiency of infection was reduced when the deletions extended to the pre-S1 domain. Overall, the results demonstrate that the activity of the pre-S domain at viral entry solely depends on the integrity of its first 75 amino acids and thus excludes any function of the matrix domain or TLM.     

A general structured model for a sequential hermaphrodite population

This paper introduces and analyzes a model of sequential hermaphroditism in the framework of continuously structured population models with sexual reproduction. The model is general in the sense that the birth, transition (from one sex to the other) and death processes of the population are given by arbitrary functions according to a biological meaningful hypotheses. The system is reduced to a single equation introducing the intrinsic sex-ratio subspace. The steady states are analyzed and illustrated for several cases. In particular, neglecting the competition for resources we have explicitly found a unique non-trivial equilibrium which is unstable.     

Pharmacological Evidence for Calcium Involvement in the Long-Term Processing of Abiotic Stimuli in Plants

Information about abiotic conditions is stored for long periods in plants and, in flax seedlings, can lead to the production of meristems. To investigate the underlying mechanism, flax seedlings were given abiotic stimuli that included a mechanical stimulus (by manipulation), one or two cold shocks, a slow cold treatment and a drought stress and, if these seedlings were then subjected to a temporary (1 to 3 days) depletion of calcium, epidermal meristems were produced in the seedling hypocotyls. This production was inhibited by the addition to the nutrient media of EGTA, ruthenium red, lanthanum or gadolinium that affect calcium availability or calcium transport. Use of these agents revealed a period of vulnerability in information processing that was less than two min for mechanical stimuli and over five min for other abiotic stimuli, consistent with information about mechanical stimuli being stored particularly fast. We propose that external calcium is needed for the transduction/storage of the information for meristem production whilst a temporary depletion of external calcium is needed for the actual production of meristems. Such roles for calcium would be consistent with a mechanism based on ion condensation on charged polymers.Key Words: memory, environmental signals, calcium, pharmacological agents, meristems, bud growth, plants