Cloning and characterization of a new polyketide synthase gene cluster in Streptomyces aureofaciens CCM 3239.

We cloned a new polyketide gene cluster, aur2, in Streptomyces aureofaciens CCM3239. Sequence analysis of the 9531-bp DNA fragment revealed 10 open reading frames, majority of which showed high similarity to the previously characterized type II polyketide synthase (PKS) genes. An unusual feature of the aur2 cluster is a disconnected organization of minimal PKS genes; ACP is located apart from the genes for ketosynthases KSalpha and KSbeta. The aur2 gene cluster was disrupted in S. aureofaciens CCM3239 by a homologous recombination, replacing the four genes (aur2A, E, F, G) including ketosynthase KSalpha, with antibiotic resistance marker gene. The disruption did not affect growth and differentiation, and disrupted strain produced spores with wild-type grey-pink pigmentation. The biochromatographic analysis of the culture extracts from S. aureofaciens wild type and aur2-disrupted strains did not reveal any difference in the pattern of antibacterial compounds.     

Characterization of chicken gizzard calcyclin and examination of its interaction with caldesmon

Using a procedure developed to purify calcyclin from mouse Ehrlich ascites tumor cells calcyclin was purified from smooth muscle of chicken gizzard. Chicken gizzard calcyclin bound to phenyl-Sepharose in a calcium dependent manner as did mouse EAT cells and rabbit lung calcyclin but appeared to be more acidic than its mammalian counterparts as revealed by ion exchange chromatography on Mono Q. Chicken gizzard calcyclin bound ⁴⁵Ca²⁺ on nitrocellulose filters and exhibited a shift in electrophoretic mobility on urea-PAGE depending on Ca²⁺ concentration. Crosslinking experiments with BS³ showed that chicken gizzard calcyclin was able to form noncovalent dimers. As indicated by a decrease in maximum tryptophan fluorescence emission of caldesmon (about 14% at 1:1 molar ratio) and displacement of calmodulin from its complex with caldesmon, chicken gizzard calcyclin binds caldesmon. This binding was, however, much weaker than that of calmodulin and could not influence the interaction of caldesmon with actin. In consequence, calcyclin was unable to reverse the inhibitory effect of caldesmon on actin-activated Mg²⁺-ATPase activity of myosin in the presence of Ca²⁺.     

Permeability of bilayer lipid membranes for superoxide (O2) radicals

Egg yolk phosphatidylcholine monolamellar liposomes (1000 Å in diameter) loaded with cytochrome c were placed into an external solution, in which superoxide radicals, O₂⁻, were generated by a xanthine-xanthine oxidase system. The penetration of the superoxide radicals across the liposomal membrane was detected by cytochrome c reduction in the inner liposome compartment. The effects of modifiers and temperature on this process were studied. The permeability of liposomal membrane for O₂⁻(P′_O2⁻ = (7.6 ± 0.3) · 10^-8 cm/s), or HO₂^• (P′_HO2⁻ = 4.9 · 10^-4 cm/s) were determined. The effect of the transmembrane electric potential (K⁺ concentration gradient, valinomycin) on the permeability of liposomal membranes for O₂⁻ were investigated. It was found that O₂⁻ can penetrate across liposomal membrane in an uncharged form. The feasibility of penetration of superoxide radicals through liposomal membrane, predominantly via anionic channels, was demonstrated by the use of an intramolecular cholesterol-amphotericin B complex.     

Pathways of lymphocyte migration within the periarterial lymphoid sheath of rat spleen

Summary Male Wistar rats were injected intravenously with 5-(³H)uridine-labeled lymphocytes isolated from lymph nodes of syngeneic donors and enriched in T cells. After short periods of time (3 to 120 min after injection), labeled lymphocytes were localized in spleen compartments using autoradiography to identify routes of lymphocyte movement from blood into splenic parenchyma and to follow migration pathways of recirculating lymphocytes within the periarterial lymphoid sheath (PALS). Topographical analysis of labeled lymphocytes was performed in specific planes of PALS characterized by the diameter of the arterial vessel and termed PALS large, PALS medium, and PALS small (PALS L, PALS M, PALS S, respectively). Attention was also paid to accumulations of labeled lymphocytes close to the arterial vessel wall. Initially, labeled lymphocytes were localized in PALS S and PALS M near the terminal branching of arterial vessels and in the marginal zone (MZ). We conclude that lymphocytes emigrate from blood into splenic parenchyma within two white pulp compartments: in MZ, and directly within PALS through the wall of capillary vessels. The sequential accumulation of labeled cells near arterial vessels of increasing diameter suggests that the recirculating pool of lymphocytes migrates into the central part of PALS L by two routes: from MZ, and along arterial vessels from PALS S and PALS M.R.B. was a fellow of the Alexander von Humboldt-Stiftung, on leave from the Department of Histology and Embryology, Institut of Biostructure, Academy of Medicine, ul. Swiecickiego 6, PL-60-781 Pozna, Poland.     

Polarity and competition between megaspores in the ovule ofOenothera hybrids

New data on the development of polarity in the ovules during megasporogenesis and early stages of embryo sac development inOenothera-hybrids are presented. It is confirmed that allOe. hookeri-hybrids show a strong tendency to form heteropolar tetrads, with the micropylar megaspore developing into an embryo sac. This preference is seen in the delay of the second meiotic division on the chalazal side, the absence of callose in the lateral wall of the micropylar megaspore, and the accumulation of starch in this megaspore. However, homopolar tetrads, chalazal preference, and ovules with two developing embryo sacs are also observed with considerable frequency. Quantitative data on the frequency of the different developmental types are compared with earlier genetic results about competition in the haplophase. There is sufficiently good agreement to support the hypothesis ofRenner that there is a correlation between the developmental processes in the megaspore tetrad and the genetic phenomena of competition in the haplophase.     

Cell interactions in the generation of chaetae pattern inDrosophila

Summary We have already shown that theachaetae-scute complex (AS-C) ofDrosophila is regulated by two genes,hairy andextramacrochaetae. Using mutants in these genes, we have analysed how different levels of expression of AS-C affect the pattern of chaetae. The results indicate that the spatial distribution of chaetae results from cell interactions, probably by a mechanism of lateral inhibition. The results are discussed in view of the different theories of pattern formation.     

On the conformational dependence of the proton chemical shifts in nucleosides and nucleotides III. Proton chemical shifts of 5′-nucleotides as a function of different conformational parameters

The variation of the chemical shift of the protons of 5′-UMP and 5′-AMP is calculated as a function of χ_CN, ψ and ? torsion angles. The shift of H8 of 5′-AMP and H6 of 5′-UMP is found to be very sensitive to the value of χ_CN. For the anti conformations the shift of these protons is more sensitive to the value of the rotation about CS′-05′ than about C4′-CS′. For the protons of the ribose the calculations show that for the C2′-endo pucker H3′ and H2′ undergo the largest chemical shift variations when ? and ψ vary. The calculated variations are considered in relation with the role of the conformation of the nucleotides in the chemical shift variation between mono and polynucleotides and between the different helical structures of polynucleotides.     

A limnological reconnaissance of Lake Tebenquiche,Salar de Atacama,Chile

A number of expeditions to the area of Salar de Atacama, Chile, 68° 15'W, 20° 30'S, have involved studies of the biological and chemical features of Lake Tebenquiche, situated in the interior of the salar. Chemically, Tebenquiche is hypersaline, with practically anoxic waters dominated by sodium and chloride ions but with high concentrations of sulphate also. The lake is surrounded and invaded by macrophytes, dominated by Scirpus olmeyi and Juncus, which provide organic material for the formation of bacterial mats. The fauna of limnetic crustaceans is almost exclusively of Artemia salina. The most important genera of bacteria are: Marinomonas, Halobacterium, Acinetobacter and the sulphur reductors Vibrio and Bacillus. The Cyanobacteria are represented exclusively by Oscillatoria.