Organotin compounds induce aneuploidy in human peripheral lymphocytes in vitro

In vitro exposure of PHA-stimulated human lymphocytes to organotin compounds resulted in statistically significant increases in the frequencies of hyperdiploid cells. When taken together with our previous study demonstrating spindle inhibiting effects of the same organotin compounds by an indirect method (Jensen et al., 1989), the present study strongly indicates that organotin compounds are able to induce aneuploidy, probably by affecting spindle function.     

Fractionation of eukaryotic DNA in a pulsating electrical field. I. Detection and properties of discrete DNA fragments]

The fractionation of eukaryotic DNA by field inversion gel electrophoresis results in the appearance of discrete DNA-fragments. The set of these fragments is similar to that of different eukaryotic representatives and consists of various chromosomal DNAs, unified by size. The physical properties of DNA-fragments suggest that they can form multimeric structures due to the presence of sticky ends flanking discrete fragments. We suppose that the set of discrete DNA-fragments results in a specific cleavage of intact nuclear DNA and can reflect different levels of chromatin structural organization.     

Immunological identification of yeast SCO1 protein as a component of the inner mitochondrial membrane

Summary The SCO1 gene of Saccharomyces cerevisiae encodes a 30 kDa protein which is specifically required for a post-translational step in the accumulation of subunits 1 and 2 of cytochrome c oxidase (COXI and COXII). Antibodies directed against a -Gal::SCO1 fusion protein detect SCO1 in the mitochondrial fraction of yeast cells. The SCO1 protein is an integral membrane protein as shown by its resistance to alkaline extraction and by its solubilization properties upon treatment with detergents. Based on the results obtained by isopycnic sucrose gradient centrifugation and by digitonin treatment of mitochondria, SCO1 is a component of the inner mitochondrial membrane. Membrane localization is mediated by a stretch of 17 hydrophobic amino acids in the amino-terminal region of the protein. A truncated SCO1 derivative lacking this segment, is no longer bound to the membrane and simultaneously loses its biological function. The observation that membrane localization of SCO1 is affected in mitochondria of a rho ⁰ strain, hints at the possible involvement of mitochondrially coded components in ensuring proper membrane insertion.     

RNA and DNA synthesis catalyzed by a DNA-polymerase alpha complex with primase from silkworm cells on single-stranded DNA]

Depending on the ionic environment the replicative complex of silkworm Bombyx mori, containing DNA polymerase alpha and primase, catalyzes on single-stranded DNA of phage M13 a NTP-dependent synthesis or elongation of preformed primers. In the presence of NTPs and dNTPs at conditions optimal for the NTP-dependent synthesis the replicative complex synthesizes on M13 DNA oligoribonucleotides of 9-11 residues, which serve as primers for polymerization of DNA. The length of RNA-primers synthesized by primase of the complex depends on concentration of dNTP but does not depend on activity of DNA polymerase alpha. During elongation of exogenic primers annealed to M13 DNA the complex is processive synthesizing DNA fragments of dozens residues without dissociation from the template. Double-stranded structures in DNA such as "hairpins" appear to be barriers for driving of the complex along the template and cause pauses in elongation. DNA-binding proteins the SSB of Escherichia coli or the p32 of phage T4 destabilize double-stranded regions in DNA and eliminate elongation pauses corresponding to these regions. The replicative complex is able to fill in single-stranded gaps in DNA completely and to perform slowly the synthesis with displacement of one of parent strands in duplexes via repeated cycles of binding to the primer-template, limited elongation and dissociation.     

Binding of SSB-protein from Ehrlich ascites carcinoma cells with DNA and polyribonucleotides]

Binding of SSB-protein from Ehrlich ascites tumor to ssDNA from M13 phage leads to its compactization. The structure of the complex at the protein/DNA ratios far from the saturation level looks like "beads-on the string". DNA that was fully saturated with protein forms collapsed globular structure. Binding of the protein to the dsDNA from phage lambda increases its flexibility and decreases the coil dimensions; no "beads-on the string" structure are seen. The protein possess slight destabilizing effect on hairpin helices of M13DNA. Competition studies demonstrate that the binding properties of protein with polyribonucleotide lattices and DNA's decrease in ranking as follows: poly(rG) greater than or equal to poly(rI) greater than or equal to ssDNA greater than dsDNA greater than poly(rA) congruent to approximately poly(rU). Thus SSB-protein from Ehrlich ascites tumor differs significantly from its presumed prokaryotic analogs.     

Contribution of organic acids to the acidification of the rhizosphere of maize seedlings

The participation of organic acids in the process of soil acidification was related to other H⁺ pumping processes. The ratio between efflux of organic acids and proton secretion of maize roots was determined with the use of a pH-stat combined with a collecting system for organic acids. Changes in the composition of carboxylic acids influenced by nitrogen supply were monitored by HPLC and via enzymatic conversion. The following substances were found to be secreted by maize roots: glycolate, glyoxylate, fumarate, 2-oxoglutarate and oxalate. Malate, however, could not be detected. There is no organic acid dominantly secreted by the roots, but changes are observed during aging which might result from deficiencies of nutrients e.g. P. Fertilization of N-deficient plants with urea leads to a significant change in the composition of acids secreted. In this case, oxalate was additionally detected with a concomitant increase in glyoxylate, indicating important changes in metabolism. Acidification of the rhizosphere is predominantly maintained by secretion of protons, not by efflux of organic acids, which contributed 0.2 to 0.3% to this process only. The role of organic acids in nutrient uptake is discussed.     

Diurnal periodicity of chalcone-synthase activity during the development of oat primary leaves

Chalcone-synthase (CHS) activity was followed during the development of primary leaves of oat (Avena sativa L.) seedlings grown under different illumination conditions. Continuous darkness and continuous light resulted in similar time courses of enzyme activity. The maximum of CHS activity in etiolated leaves was delayed by 1 d and reached about half the level of that of light-grown leaves. In seedlings grown under defined light-dark cycles a diurnal rhythm of CHS activity and its protein level was observed which followed the rhythm of CHS-mRNA translational activity (Knogge et al. 1986). This rhythm persisted in continuous light after a short-term pre-exposure to the light-dark cycle but not in continuous darkness.Abbreviations CHS chalcone synthase - PAL phenylalanine ammonio lyase Financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged (G.W., We 630/9-7; We 630/10-1). Thanks are given to Dr. St. Kellam (Department of Plant Microbiological Sciences, University of Canterbury, New Zealand) for correcting the English.