Mirrored Genome Size Distributions in Monocot and Dicot Plants

The variation in genome size and basic chromosome number was analyzed in the wide range of angiosperm plants. A divergence of monocots vs. dicots (eudicots) genome size distributions was revealed. A similar divergence was found for annual vs. perennial dicots. The divergence of monocots vs. dicots genome size distributions holds at different taxonomic levels and is more pronounced for species with larger genomes. Using nested analysis of variance, it was shown that putative constraints on genome size variation are not only stronger in dicots as compared to monocots but in the former they start to operate already at the family level, whereas in the latter they do so only at the order level. At the same time, variation in basic chromosome number is constrained at the order level in both groups. Higher basic chromosome numbers were found in perennial plants as compared to the annual ones, which can be explained by their need for a higher genetic recombination as compensation for the longer life-cycles. A negative correlation was found between genome size and basic chromosome number, which can be explained as a trade-off between different recombination mechanisms.     

Isolation and properties of plastocyanin from Anabaena variabilis

Plastocyanin is a copper protein found in photosynethetic tissue and it exhibits the properties of a physiological redox reagent. This protein has been purified from the blue-green alga Anabaena variabilis. Plastocyanin is required for a number of partial reactions of the photosynthetic electron transfer chain. These reactions include the transfer of electrons from reduced 2,3′,6-trichlorophenolindophenol,N,N,N′,N′- tetramethyl-p-phenylenediamine and 2,3,5,6-tetramethyl-p-phenylenediamine to low potential oxidants. Reduced cytochrome c photooxidation does not appear to be dependent on plastocyanin. Cytochrome f, isolated from this alga, will partially replace plastocyanin in many of these reations. Inhibition of photosynthetic reactions by copper chelators appears to occur at some site other than the site of plastocyanin function.     

Peptide loading in the endoplasmic reticulum accelerates trafficking of peptide: MHC class II complexes in B cells

In a combination of biochemical and immunoelectron-microscopical approaches we studied intracellular trafficking and localization of the endoplasmic-reticulum (ER)-formed complexes of murine MHC class II molecule I-A^b and an antigenic peptide E52–68 covalently linked to its -chain. The association with the peptide in the ER leads to sharp acceleration of the intracellular trafficking of the complexes to the plasma membrane. Within the cells, E52–68:I-A^b complexes accumulate in the multivesicular MHC class II compartment (MIIC), but not in denser multilaminar or intermediate type MIICs. The changes in the trafficking of ER-formed complexes result solely from the presence of the tethered peptide, since wild-type class II molecules traffic similarly in bare lymphocyte syndrome cells and in wild-type antigen-presenting cells.     

Phytotoxicity of selected trichothecenes using Chlamydomonas reinhardtii as a model systemt

Trichothecenes are potent inhibitors of cytoplasmic protein synthesis which can affect the severity of plant diseases such as wheat head scab. While many trichothecene-producing fungi share the initial biosynthetic intermediates, Fusarium sp. are unique in the production of trichothecenes containing an oxygen function at C-3. Although the initial trichothecene and the final products have a C-3 hydroxyl group, the intermediate steps are acetylated at C-3. By using Chlamydomonas reinhardtii, a unicellular plant with a well-defined genetic system, we were able to test the proposal that trichothecenes with a C-3 hydroxyl are more toxic to plants, as well as demonstrate that C. reinhardtii is a promising plant trichothecene bioassay system. Seven pairs of trichothecenes with either a C-3 hydroxyl or C-3 acetyl group were assayed. Our results confirm that trichothecenes acetylated at C-3 were far less toxic to Chlamydomonas than those with a C-3 hydroxyl group.     

Purification and properties of pyrophosphatase of Acinetobacter johnsonii 210A and its involvement in the degradation of polyphosphate

Inorganic pyrophosphatase (E.C. 3.6.1.1) of Acinetobacter johnsonii210A was purified 200-fold to apparent homogeneity. The enzyme catalyzedthe hydrolysis of inorganic pyrophosphate and triphosphate to orthophosphate.No activity was observed with other polyphosphates and a wide variety oforganic phosphate esters. The molecular mass of the enzyme was estimatedto be 141 kDa by gelfiltration. Sodium dodecyl sulfate-polyacrylamide gelelectrophoresis indicated a subunit composition of six identical polypeptideswith a molecular mass of 23 kDa. The cation Mg² was required foractivity, the activity with Mn², Co² and Zn² was 48, 48 and 182% of the activity observed with Mg², respectively. The enzyme was heat-stable and inhibited by fluoride and iodoacetamide. The analysis of the kinetic properties of the enzyme revealed an apparent K_m for pyrophosphate of 0.26 mM. In A. johnsonii 210A, pyrophosphatase may be involved in the degradation of high-molecular polyphosphates under anaerobic conditions: (i) it catalyses the further hydrolysis of pyrophosphate and triphosphate formed from high-molecular weight polyphosphates by the action of exopolyphosphatase, and (ii) it abolishes the inhibition of polyphosphate: AMP phosphotransferase-mediated degradation by pyrophosphate and triphosphate.     

Aluminium hydroxide adjuvant initiates strong antigen-specific Th2 responses in the absence of IL-4- or IL-13-mediated signaling

Previous studies demonstrate that aluminium hydroxide adjuvant (alum) produces increased Th1 responses in IL-4-deficient mice compared with wild-type animals, although the continued production of IL-5 by spleen cells from these mice also indicates that Th2 responses are induced. In the present study, we demonstrate that alum can induce Th2-associated IL-4 and IL-5 production in the absence of IL-4 signaling in mice deficient in either IL-4Ralpha or Stat6. The Th2 responses observed could not be due to IL-13 as IL-13 responses are also impaired in IL-4Ralpha- and Stat6-deficient mice. We also detected higher levels of IL-4 in IL-4Ralpha gene-deficient, though not Stat6-deficient, mice compared with their wild-type counterparts. The increased levels of IL-4 could be explained by the IL-4R being unavailable to neutralize this cytokine in IL-4Ralpha-deficient mice. While levels of IL-5 production in IL-4Ralpha- or Stat6-deficient mice were similar to IL-4-deficient and wild-type mice, other type 2-associated responses, which are largely or wholly IL-4 dependent, such as the production of IgG1 or IgE Abs, were either reduced or absent. We conclude that alum adjuvants can induce IL-4 production and Th2 responses independently of IL-4 or IL-13, negating the requirement for an early source of IL-4 in the Th2 response induced by this adjuvant.     

Hydrogen bonding and equilibrium protium-deuterium fractionation factors in the immunoglobulin G binding domain of protein G

Protium-deuterium fractionation factors (phi) were determined for more than 85% of the backbone amide protons in the IgG binding domains of protein G, GB1 and GB2, from NMR spectra recorded over a range of H2O/D2O solvent ratios. Previous studies suggest a correlation between phi and hydrogen bond strength; amide and hydroxyl groups in strong hydrogen bonds accumulate protium (phi < 1), while weak hydrogen bonds accumulate deuterium (phi > 1). Our results show that the alpha-helical residues have slightly lower phi values (1.03 +/- 0.05) than beta-sheet residues (1.12 +/- 0.07), on average. The lowest phi value obtained (0.65) does not involve a backbone amide but rather is for the interaction between two side chains, Y45 and D47. Fractionation factors for solvent-exposed residues are between the alpha-helix and beta-sheet values, on average, and are close to those for random coil peptides. Further, the difference in phiav between alpha-helix and solvent-exposed residues is small, suggesting that differences in hydrogen bond strength for intrachain hydrogen bonds and amide...water hydrogen bonds are also small. Overall, the enrichment for deuterium suggests that most backbone...backbone hydrogen bonds are weak.     

Disruption of TRI101, the gene encoding trichothecene 3-O-acetyltransferase, from Fusarium sporotrichioides

We screened a Fusarium sporotrichioides NRRL 3299 cDNA expression library in a toxin-sensitive Saccharomyces cerevisiae strain lacking a functional PDR5 gene. Fourteen yeast transformants were identified as resistant to the trichothecene 4,15-diacetoxyscirpenol, and each carried a cDNA encoding the trichothecene 3-O-acetyltransferase that is the F. sporotrichioides homolog of the Fusarium graminearum TRI101 gene. Mutants of F. sporotrichioides NRRL 3299 produced by disruption of TRI101 were altered in their abilities to synthesize T-2 toxin and accumulated isotrichodermol and small amounts of 3, 15-didecalonectrin and 3-decalonectrin, trichothecenes that are not observed in cultures of the parent strain. Our results indicate that TRI101 converts isotrichodermol to isotrichodermin and is required for the biosynthesis of T-2 toxin.