A single domain of the replication termination protein of Bacillus subtilis is involved in arresting both DnaB helicase and RNA polymerase

The current models that have been proposed to explain the mechanism of replication termination are (i) passive arrest of a replication fork by the terminus (Ter) DNA-terminator protein complex that impedes the replication fork and the replicative helicase in a polar fashion and (ii) an active barrier model in which the Ter-terminator protein complex arrests a fork not only by DNA-protein interaction but also by mechanistically significant terminator protein-helicase interaction. Despite the existence of some evidence supporting in vitro interaction between the replication terminator protein (RTP) and DnaB helicase, there has been continuing debate in the literature questioning the validity of the protein-protein interaction model. The objective of the present work was two-fold: (i) to reexamine the question of RTP-DnaB interaction by additional techniques and different mutant forms of RTP, and (ii) to investigate if a common domain of RTP is involved in the arrest of both helicase and RNA polymerase. The results validate and confirm the RTP-DnaB interaction in vitro and suggest a critical role for this interaction in replication fork arrest. The results also show that the Tyr(33) residue of RTP plays a critical role both in the arrest of helicase and RNA polymerase.     

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.     

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.