Showing papers by "Spanish National Research Council published in 1987"

Phase equilibria of fluid interfaces and confined fluids

Abstract: Phase transitions at fluid interfaces and in fluids confined in pores have been investigated by means of a density functional approach that treats attractive forces between fluid molecules in mean-field approximation and models repulsive forces by hard-spheres. Two types of approximation were employed for the hard-sphere free energy functional: (a) the well-known local density approximation (LDA) that omits short-ranged correlations and (b) a non-local smoothed density approximation (SDA) that includes such correlations and therefore accounts for the oscillations of the density profile near walls. Three different kinds of phase transition were considered: (i) wetting transition. The transition from partial to complete wetting at a single adsorbing wall is shifted to lower temperatures and tends to become first-order when the more-realistic SDA is employed. Comparison of the results suggests that the LDA overestimates the contact angle γ in a partial wetting situation. (ii) capillary evaporation of a fluid...

Homology between Streptomyces genes coding for synthesis of different polyketides used to clone antibiotic biosynthetic genes

Abstract: Many important antibiotics such as tetracyclines, erythromycin, adriamycin, monensin, rifamycin and avermectins are polyketides. In their biosynthesis, multifunctional synthases1 catalyse iterated condensation of thio-esters derived from acetate, propionate or butyrate to yield aliphatic chains of varying length and carrying different alkyl substituents. Subsequent modifications, including aromatic or macrolide ring closure or specific methylations or glycosylations, generate further chemical diversity. It has been suggested that, if different polyketide synthases had a common evolutionary origin, cloned DNA coding for one synthase might be used as a hybridization probe for the isolation of others2. We show here that this is indeed possible. Study of a range of such synthase genes and their products should help to elucidate what determines the choice and order of condensation of different residues in polyketide assembly, and might yield, by in vitro recombination or mutagenesis, synthase genes capable of producing novel antibiotics3. Moreover, because genes for entire antibiotic pathways are usually clustered in Streptomyces4, cloned polyketide synthase genes are valuable in giving access to groups of linked biosynthetic genes.

Vesicular‐arbuscular mycorrhiza improve both symbiotic n2 fixation and n uptake from soil as assessed with a 15n technique under field conditions

Abstract: Summary A technique using 15N-labelled inorganic fertilizer was applied to estimate N2 fixation by the forage legume Hedysarum coronarium L. and to ascertain the role of vesicular-arbuscular (VA) mycorrhizas in plant N nutrition throughout a growing season under field conditions. The absence of the specific Rhizobium for the forage legume in the test soil allowed us the use of 15N methodology with the same legume as reference ‘non-fixing’ crop. At the first harvest, mycorrhizal inoculation behaved similarly to the phosphate addition in improving the percentage (70 %) and the total amount of N derived from fixation. But thereafter, mycorrhizal inoculation not only enhanced dry matter yield, N concentration and total N yield but also the amount of N derived from soil and from fixation, as compared with either phosphate-added or control plants. This indicated that mycorrhizas acted both by a P-mediated mechanism to improve N2 fixation and by enhancing N uptake from soil. The latter agrees with recent findings by others that VA mycorrhizal hyphae can translocate and assimilate ammonium, a fact of physiological and ecological interest.

Monte Carlo simulations for scattering of electromagnetic waves from perfectly conductive random rough surfaces.

Abstract: Numerical calculations of mean scattered intensities by simulation of one-dimensional perfectly conductive random rough surfaces are presented Results relative to backscattering enhancement and more accurate criteria for the validity of the Kirchhoff approximation are obtained This method can also be used for assessing perturbative theories and for further experiments

Molecular organization of the maternal effect region of the Shaker complex of Drosophila: characterization of an IA channel transcript with homology to vertebrate Na+ channel

Abstract: We have cloned 215-kb DNA containing the maternal effect region (ME) of the Shaker gene complex (shC) at 16F of the Drosophila X chromosome. Five translocation and deletion breakpoints have been mapped on the cloned DNA allowing a correlation of the genetic map to transcription units. The ME region spans ˜100 kb. The genetic behavior of this region correlates with the occurrence of maternal RNAs in this part of the ShC. Two transcripts have been identified in the vicinity of chromosomal rearrangements which cause a Sh phenotype. These are a 4.5-kb transcript interrupted by T(x;2)B27 and a 2-kb transcript interrupted by T(X;3)ShLC and T(X;Y)W32. The latter transcript is derived from a primary transcript which spans >65 kb genomic DNA. The cDNA-sequencing data show that this Shaker (IAchannel) gene can encode a protein of ˜35 kd with three α-helical membrane-spanning sequences near its carboxyl terminus. These have a striking homology with membrane-spanning sequences of the vertabrate Na+ channel.

Structural and functional relationships between prokaryotic and eukaryotic DNA polymerases.

Abstract: The Bacillus subtilis phage luminal diameter 29 DNA polymerase, involved in protein-primed viral DNA replication, was inhibited by phosphonoacetic acid (PAA), a known inhibitor of alpha-like DNA polymerases, by decreasing the rate of elongation. Three highly conserved regions of amino acid homology, found in several viral alpha-like DNA polymerases and in the luminal diameter 29 DNA polymerase, one of them proposed to be the PAA binding site, were also found in the T4 DNA polymerase. This prokaryotic enzyme was highly sensitive to the drugs aphidicolin and the nucleotide analogues butylanilino dATP (BuAdATP) and butylphenyl dGTP (BuPdGTP), known to be specific inhibitors of eukaryotic alpha-like DNA polymerases. Two potential DNA polymerases from the linear plasmid pGKL1 from yeast and the S1 mitochondrial DNA from maize have been identified, based on the fact that they contain the three conserved regions of amino acid homology. Comparison of DNA polymerases from prokaryotic and eukaryotic origin showed extensive amino acid homology in addition to highly conserved domains. These findings reflect evolutionary relationships between hypothetically unrelated DNA polymerases.

Identification of components of a new stability system of plasmid R1, ParD, that is close to the origin of replication of this plasmid.

Abstract: We provide evidence that a mutation which derepresses an autoregulated system that is located in the vicinity of the basic replicon of R1, stabilizes the ParA- and ParB- miniplasmid of R1 pKN1562, without increasing its copy number. The system, which we have called ParD, maps inside the 1.45-kb PstI-EcoRI fragment that is adjacent to the origin of replication of the plasmid. Two proteins whose expression is coordinated are components of the system. The sequence of the PstI-EcoRI fragment was obtained. The wild-type ParD system determines in cis a basal but detectable stability.

Replacement of the promoter of the yeast plasma membrane ATPase gene by a galactose-dependent promoter and its physiological consequences

Abstract: In order to probe the physiological role of the yeast plasma membrane ATPase we have replaced the constitutive promoter of its gene by a galactose-dependent promoter. The resulting cells stop growing on glucose medium when the preformed ATPase is diluted to 20% of normal. There is a correlation between ATPase activity and both proton efflux from the cells and amino acid transport. A large proportion of growth-arrested cells appear enlarged and with several buds containing nuclei.

Biological role of the pneumococcal amidase. Cloning of the lytA gene in Streptococcus pneumoniae.

Abstract: A pneumococcal recombinant plasmid, pRG2, containing the lytA gene that codes for the pneumococcal N-acetylmuramoyl-L-alanine amidase has been constructed using the pneumococcal plasmid pLS1 as a vector. pRG2 was introduced by genetic transformation into a mutant of Streptococcus pneumoniae (M31) that has a complete deletion of the lytA gene. The transformed strain (M51) grew at a normal growth rate as 'diplo' cells and underwent autolysis at the end of the exponential phase of growth, two properties that had been lost in the deleted mutant M31. M51 lysed very rapidly at the end of the exponential phase when the cells were grown in choline-containing medium probably because of the higher level of amidase activity present in this strain as compared to the lysis-prone strain M11. These findings show that the expression of the plasmid-linked gene was placed under the mechanism(s) of control of the cell during the exponential phase. Our results demonstrate that the physiological role of the pneumococcal amidase was to catalyze the separation of the daughter cells at the end of the cell division to produce diplo cells; in addition we have also confirmed the basic role of this autolysin in the bacteriolytic nature of beta-lactam antibiotics.

Involvement of the CD4 molecule in a post-activation event on T cell proliferation.

Abstract: A monoclonal antibody (mAb) directed to a human leukocyte 55-kDa cell surface molecule with identical cellular distribution and biochemical properties to the CD4 was able to inhibit T cell proliferation induced either in a mixed lymphocyte culture or by activation with mAb anti-CD3, anti-CD2 or phytohemagglutinin. The inhibitory effect of anti-CD4 was observed in the absence of monocytes and was directly exerted on T4+ cells. This effect on cellular proliferation appears to be due to an inhibition of a post-activation event since (a) the rise of cytoplasmic Ca2+ after activation with anti-CD3 mAb is not affected by the presence of anti-CD4 and (b) the proliferation that occurs after an activation pulse of 3 h with ionophore and phorbol myristate acetate can be inhibited when the anti-CD4 is added after the pulse period. Kinetic studies demonstrated that the inhibition of cellular proliferation by anti-CD4 mAb was observed even if the antibody was added as late as 18–24 h after the initiation of the culture. The effect of this blocking anti-CD4 mAb on the interleukin (IL) 2/IL 2 receptor signalling pathways was also examined. The presence of anti-CD4 slightly affected the production of IL 2. In fact, addition of exogenous recombinant IL 2 at the initiation of the cultures did not restore the proliferative response. However, anti-CD4 had a strong inhibitory effect on the expression of IL 2 receptors as analyzed by direct immunofluorescence cytometry. Taken together, these results indicate that the binding of the anti-CD4 mAb to T cells interferes with a late metabolic step being capable of abolishing the proliferative activity of fully activated cells.

Bacterial flora in bottled uncarbonated mineral drinking water

Abstract: A quantitative study of bacterial populations in mineral water was carried out. Samples were stored at 6 and 20 °C, and the colony counts were determined on tryptone agar plates incubated at 22 and...