Isolation of (−)-cryptosporiopsin,a chlorinated cyclopentenone fungitoxic metabolite fromPhialophora asteris f. sp.helianthi

Summary The (–)-enantiomer of cryptosporiopsin, a chlorinated cyclopentenone fungitoxic metabolite, was isolated fromPhialophora asteris f. sp.helianthi. Next to a comparable fungitoxic activity as shown by crypstosporiopsin, the product particularly inhibits growth ofSclerotinia sclerotiorum, an important pathogen on sunflower. Two further metabolites were tentatively identified as a stereoisomer of cryptosporiopsin and its dehydrated derivative.The authors are much indebted to Dr.G. M. Strunz (Canadian Forestry Service) for valuable suggestions and the generous gift of cryptosporiopsin and to the University of Utrecht for the part-time fellowship to one of us (Y.T.) given.     

Actin-based motility of vaccinia virus mimics receptor tyrosine kinase signalling.

Studies of the actin-based motility of the intracellular pathogens Listeria monocytogenes and Shigella flexneri have provided important insight into the events occurring at the leading edges of motile cells. Like the bacteria Listeria and Shigella, vaccinia virus, a relative of the causative agent of smallpox, uses actin-based motility to spread between cells. In contrast to Listeria or Shigella, the actin-based motility of vaccinia is dependent on an unknown phosphotyrosine protein, but the underlying mechanism remains obscure. Here we show that phosphorylation of tyrosine 112 in the viral protein A36R by Src-family kinases is essential for the actin-based motility of vaccinia. Tyrosine phosphorylation of A36R results in a direct interaction with the adaptor protein Nck and the recruitment of the Ena/VASP family member N-WASP to the site of actin assembly. We also show that Nck and N-WASP are essential for the actin-based motility of vaccinia virus. We suggest that vaccinia virus spreads by mimicking the signalling pathways that are normally involved in actin polymerization at the plasma membrane.     

Emericid,a new polyether antibiotic fromStreptomyces hygroscopicus (DS 24 367)

Summary Emericid is a new polyether polycyclic ionophore antibiotic excreted byStreptomyces hygroscopicus (DS 24 367). Active in vitro against Gram-positive bacteria, it is ineffective in vivo. At a 0.006–0.02% level in the diet it protects chickens and rabbits against coccidiosis.From a recent paper byN. Otake (Tetrahedron Lett.1970, 4147) emericid and lonomycin would be identical.     

Quantitative determination of the activity of acid peptidases of industrial origin]

Reagent ninhydrine-Cd++, reacts with free alpha and epsilon amino groups of proteins. Horse-heart apomyoglobin was subjected to exhaustive succinylation, rendering the product non reactive to ninhydrine. The succinylglobin was submitted to enzyme digestion at pH 2.0, 4.0, 4.7 and 6.0. The commercially available enzymes contain mainly pepsin-like and chymosin-like enzymes. The enzymatic digests of succinyl-globin contain new free alpha-amino groups reacting with ninhydrin. Enzymatic digestion was performed under various condition (ratio E/S, pH). The results were compared to those obtained with synthetic substrate: PRO-HIS-LEU-SER-PHE(NO2)-NLEU-ALA-LEU-OME. The price of the synthetic substrate used, was more than 100 times the cost of succinyl-globin, thus the use of this substrate is a valuable tool for the quantitative estimation of peptidase activity in commercially available (pepsin, chymosin-like) enzymes.     

“Controlled” and “Living” Cationic Polymerizations:Another Way Towards Well Defined Polymer Architectures and Materials

1 Results No doubt that one of the major breakthroughs in polymer chemistry was the discovery and the progressive implementation of the “living“ and “controlled“ polymerizations.These now widely used techniques allow not only to control with an extreme precision the molar masses and their distributions but also to synthesise easily a broad variety of architectures from block and graft copolymers,miktoarms stars,to polymer brushes,hyperbranched polymers,dendrimers,etc....They opened an immense domain of ...     

XCDT1 is required for the assembly of pre-replicative complexes in Xenopus laevis

In eukaryotic cells, chromosomal DNA replication begins with the formation of pre-replication complexes at replication origins. Formation and maintenance of pre-replication complexes is dependent upon CDC6 (ref. 1), a protein which allows assembly of MCM2-7 proteins, which are putative replicative helicases. The functional assembly of MCM proteins into chromatin corresponds to replication licensing. Removal of these proteins from chromatin in S phase is crucial in origins firing regulation. We have identified a protein that is required for the assembly of pre-replication complexes, in a screen for maternally expressed genes in Xenopus. This factor (XCDT1) is a relative of fission yeast cdt1, a protein proposed to function in DNA replication, and is the first to be identified in vertebrates. Here we show, using Xenopus in vitro systems, that XCDT1 is required for chromosomal DNA replication. XCDT1 associates with pre-replicative chromatin in a manner dependent on ORC protein and is removed from chromatin at the time of initiation of DNA synthesis. Immunodepletion and reconstitution experiments show that XCDT1 is required to load MCM2-7 proteins onto pre-replicative chromatin. These findings indicate that XCDT1 is an essential component of the system that regulates origins firing during S phase.