An infrared ring around the magnetar SGR 1900+14

Magnetars are a special class of slowly rotating (period approximately 5-12 s) neutron stars with extremely strong magnetic fields (>10(14 )G)--at least an order of magnitude larger than those of the 'normal' radio pulsars. The potential evolutionary links and differences between these two types of object are still unknown; recent studies, however, have provided circumstantial evidence connecting magnetars with very massive progenitor stars. Here we report the discovery of an infrared elliptical ring or shell surrounding the magnetar SGR 1900+14. The appearance and energetics of the ring are difficult to interpret within the framework of the progenitor's stellar mass loss or the subsequent evolution of the supernova remnant. We suggest instead that a dust-free cavity was produced in the magnetar environment by the giant flare emitted by the source in August 1998. Considering the total energy released in the flare, the theoretical dust-destruction radius matches well with the observed dimensions of the ring. We conclude that SGR 1900+14 is unambiguously associated with a cluster of massive stars, thereby solidifying the link between magnetars and massive stars.     

Structure of the guide-strand-containing argonaute silencing complex

The slicer activity of the RNA-induced silencing complex is associated with argonaute, the RNase H-like PIWI domain of which catalyses guide-strand-mediated sequence-specific cleavage of target messenger RNA. Here we report on the crystal structure of Thermus thermophilus argonaute bound to a 5'-phosphorylated 21-base DNA guide strand, thereby identifying the nucleic-acid-binding channel positioned between the PAZ- and PIWI-containing lobes, as well as the pivot-like conformational changes associated with complex formation. The bound guide strand is anchored at both of its ends, with the solvent-exposed Watson-Crick edges of stacked bases 2 to 6 positioned for nucleation with the mRNA target, whereas two critically positioned arginines lock bases 10 and 11 at the cleavage site into an unanticipated orthogonal alignment. Biochemical studies indicate that key amino acid residues at the active site and those lining the 5'-phosphate-binding pocket made up of the Mid domain are critical for cleavage activity, whereas alterations of residues lining the 2-nucleotide 3'-end-binding pocket made up of the PAZ domain show little effect.     

Discovery of the first Asian plethodontid salamander

Nearly 70% of the 535 species of salamanders in the world are members of a single family, the Plethodontidae, or lungless salamanders. The centre of diversity for this clade is North and Middle America, where the vast majority (99%) of species are found. We report the discovery of the first Asian plethodontid salamander, from montane woodlands in southwestern Korea. The new species superficially resembles members of North American genera, in particular the morphologically conservative genus Plethodon. However, phylogenetic analysis of the nuclear encoded gene Rag-1 shows the new taxon to be widely divergent from Plethodon. The new salamander differs osteologically from putative relatives, especially with respect to the tongue (attached protrusible) and the derived tarsus. We place the species in a new genus on the basis of the morphological and molecular data. The distribution of the new salamander adds to the enigma of Old World plethodontids, which are otherwise restricted to the western Mediterranean region, suggesting a more extensive past distribution of the family.     

Structural basis for 5'-end-specific recognition of guide RNA by the A. fulgidus Piwi protein

RNA interference (RNAi) is a conserved sequence-specific gene regulatory mechanism mediated by the RNA-induced silencing complex (RISC), which is composed of a single-stranded guide RNA and an Argonaute protein. The PIWI domain, a highly conserved motif within Argonaute, has been shown to adopt an RNase H fold critical for the endonuclease cleavage activity of RISC. Here we report the crystal structure of Archaeoglobus fulgidus Piwi protein bound to double-stranded RNA, thereby identifying the binding pocket for guide-strand 5'-end recognition and providing insight into guide-strand-mediated messenger RNA target recognition. The phosphorylated 5' end of the guide RNA is anchored within a highly conserved basic pocket, supplemented by the carboxy-terminal carboxylate and a bound divalent cation. The first nucleotide from the 5' end of the guide RNA is unpaired and stacks over a conserved tyrosine residue, whereas successive nucleotides form a four-base-pair RNA duplex. Mutation of the corresponding amino acids that contact the 5' phosphate in human Ago2 resulted in attenuated mRNA cleavage activity. Our structure of the Piwi-RNA complex, and that determined elsewhere, provide direct support for the 5' region of the guide RNA serving as a nucleation site for pairing with target mRNA and for a fixed distance separating the RISC-mediated mRNA cleavage site from the anchored 5' end of the guide RNA.     

Lectin-like polypeptides of P. falciparum bind to red cell sialoglycoproteins

Attempts to control human malaria by immunological means could be compromised by antigenic variability within and between different strains of malarial parasites1. A useful alternative approach might be to block parasite antigens which are important in the mechanisms of invasion of red cells. As the major human parasite Plasmodium falciparum is highly specific for human red cells, isolation of the proteins involved in the recognition of red cells by this parasite might be of particular value. Recent studies suggest that the major red cell sialoglycoproteins (SGPs), glycophorins A, B and possibly C, may carry the sites recognized by the parasite2-4. Furthermore, because certain carbohydrates present on SGPs such as N-acetylglucosamine are able to block invasion by the parasite5, they may be involved in the initial interaction between parasite and red cell. We have now identified parasite proteins which bind to SGP or N-acetylglucosamine on Sepharose 4B columns. Three proteins, of molecular weights (MWs) 140,000 (140K), 70K and 35K, seem to be specifically bound by N-acetylglucosamine.     

Ethanol influence on insulin secretion from isolated rat islets

Summary This study was done to delineate the role of - and -adrenergic receptors and cyclic AMP in the mechanism of ethanol effects on insulin release from isolated islets. Rats were given an -adrenergic blocker, phentolamine, or a -adrenergic blocker, propranolol. In addition, ethanol 1 g/kg was given intragastrically 1 h prior to sacrifice. Glucose mediated insulin release from isolated islets was enhanced by phentolamine and decreased by propranolol. Ethanol treatment inhibited glucose-induced insulin release from isolated islets of control rats as well as those given phentolamine and/or propranolol. Insulin release from isolated islets in response to dibutyryl-cyclic AMP was attenuated by ethanol. Theophylline enhanced glucose mediated insulin release from control islets but ethanol treatment produced a significant inhibition of insulin response. The data suggest that the site of action of the deleterious effects of ethanol on insulin release from isolated islets in rat does not involve adrenergic system and cyclic AMP.Supported by the U.S. Veterans Administration     

无血清动物细胞培养基的研制及大规模动物细胞培养新技术应用

本课题通过引进技术，开发生产替代小牛血清、胎牛血清的无血清或低血清动物细胞培养基，引进先进的动物细胞培养技术，建立中空纤维细胞反应器培养技术，从而实现动物细胞无血清、连续化大规模的生产，将对生物工程、生物医药、疫苗生产等领域的应用有着重要意义。