Secular variation in carbon isotope ratios from Upper Proterozoic successions of Svalbard and East Greenland

Analyses of stratigraphically continuous suites of samples from Upper Proterozoic sedimentary successions of East Greenland, Spitsbergen and Nordaustlandet (Svalbard) provide an approximation to the secular variation in carbon isotope ratios during a geologically and biologically important period of change from around 900 million years ago to the beginning of the Cambrian period. Late Riphean carbonates and organic material show a stratigraphically useful pattern of enrichment in 13C relative to Phanerozoic or earlier Proterozoic samples. Isotopic compositions of isolated samples from other localities are consistent with a worldwide extended interval of enhanced organic burial and consequent net survival of oxidized material, probably O2, just before the initial radiation of metazoans.     

Ecdysteroids: possible candidates for the hormone which triggers salivary gland degeneration in the ixodid tickAmblyomma hebraeum

Summary Following engorgement, female ixodid ticks secrete a tick salivary gland degeneration factor (TSGDF) into the hemolymph. Here we show that the arthropod ecdysteroid hormones, ecdysome and 20-hydroxyecdysone, induce degeneration of tick salivary glands maintained in organ culture. The effective dose range in vitro is 30–300 ng/ml, a range reported to be physiological for this species following repletion. In addition, infusion of 20-hydroxyecdysome in vivo induces salivary gland degeneration. We therefore propose that TSGDF may be an ecdysteroid.Acknowledgments. Some of the data reported here were presented to the annual meeting of the Canadian Society of Zoologists, 15–18 May 1983; Program of abstracts, page 53. Financial support of the Canadian National Sportsmen's Fund and NSERC Canada to W.R.K. is gratefully acknowledged.     

Inheritance and expression ofEsterase-1 allozymes inPeromyscus leucopus

Summary We analyzed inheritance of 5Es-1 alleles inP. leucopus and found them to be co-dominant and segregating from a single autosomal locus, thereby verifying assumptions of Mendelian inheritance imfield data. We also described an allele that is silent in hemolysate, but is active in liver extract.Acknowledgment. Laboratory analysis was partially supported by a grant-in-aid (No. 0171-02-240-76) to Kaufman from the Research Foundation of State University of New York.     

Chemistry of ion coordination and hydration revealed by a K+ channel-Fab complex at 2.0 A resolution.

Ion transport proteins must remove an ion's hydration shell to coordinate the ion selectively on the basis of its size and charge. To discover how the K+ channel solves this fundamental aspect of ion conduction, we solved the structure of the KcsA K+ channel in complex with a monoclonal Fab antibody fragment at 2.0 A resolution. Here we show how the K+ channel displaces water molecules around an ion at its extracellular entryway, and how it holds a K+ ion in a square antiprism of water molecules in a cavity near its intracellular entryway. Carbonyl oxygen atoms within the selectivity filter form a very similar square antiprism around each K+ binding site, as if to mimic the waters of hydration. The selectivity filter changes its ion coordination structure in low K+ solutions. This structural change is crucial to the operation of the selectivity filter in the cellular context, where the K+ ion concentration near the selectivity filter varies in response to channel gating.     

Structure of pre-pro-von Willebrand factor and its expression in heterologous cells

Von Willebrand factor (vWF), a multifunctional haemostatic glycoprotein derived from endothelial cells and megakaryocytes, mediates platelet adhesion to injured subendothelium and binds coagulation factor VIII in the circulation. Native vWF is a disulphide-bonded homopolymer; the monomeric subunits, of apparent relative molecular mass (Mr) 220,000 (220K) are derived from an intracellular precursor estimated at 260-275K. Multimer assembly is preceded by the formation of dimers, linked near their C-termini, which then assemble into filamentous polymers. The importance of the removal of the large vWF pro-polypeptide during multimer assembly, and whether this or other stages of the complex post-translational processing require components specific to endothelial cells or megakaryocytes, is unknown. Here we report an analysis of the complete sequence of pre-pro-vWF and expression of the molecule in heterologous cells. The vWF precursor is composed of several repeated subdomains. When expressed in COS and CHO cells, it is cleaved and assembled into biologically active high relative molecular mass disulphide bonded multimers. This suggests that the information for assembly of this complex molecule resides largely within its primary structure.     

Purification and structural characterisation of human HLA-linked B-cell antigens.

The human B cell-specific alloantigen which is closely linked genetically to HLA contains two non-covalently associated, sialogycoprotein subunits of molecular weight (MW) 29,000 (p29), and 34,000 (p34). Although p29 and p34 have different amino-terminal sequences, their tyrosine peptide maps indicate considerable similarity in other portions of their polypeptide chains. Thus the genes for their proteins may have evolved by duplication of a common ancestral gene. Another lymphocyte cell surface protein of MW 16,000 (p16) has also been characterised. Both p16 and p44 (the heavy chain of HLA-A,B antigens) have been compared with p29 and p34.     

Molecular characterization and expression of the gene encoding human erythroid-potentiating activity

Erythropoietin is the primary physiological regulator of erythropoiesis; however, in vitro studies have identified another class of mediators which appear to be important in stimulating erythroid progenitors. These factors have generally been referred to as burst-promoting activities (BPA), because they stimulate the growth of early erythroid progenitors referred to as burst-forming units-erythroid (BFU-E) which give rise to colonies of up to thousands of haemoglobinized cells. We recently reported purification of a burst-promoting activity from medium conditioned by the Mo T-lymphoblast cell line infected with human T-cell lymphotropic virus type II (HTLV-II). This purified glycoprotein of relative molecular mass (Mr) 28,000 also stimulates colony formation by more mature erythroid precursors (CFU-E) and is therefore referred to as erythroid-potentiating activity (EPA). Purified EPA specifically stimulates human and murine cells of the erythroid lineage, unlike murine interleukin-3 (IL-3) which stimulates precursor cells from all haematopoietic lineages. We report here the isolation of a complementary DNA molecular clone encoding EPA and its use in producing EPA in COS (monkey) cells and CHO (Chinese hamster ovary) cells. We also define the organization of the EPA gene in human DNA.     

Genetic engineering of factor VIII

Genetic manipulation of mammalian cells has provided a means of producing unlimited quantities of a high purity, virus-free preparation of factor VIII--the most complex protein manufactured through rDNA technology to date.     

Phospholipase C-induced neural tube defects in the mouse embryo

Summary Mouse embryo neurulae were exposed in vitro to phospholipase C to examine the role of carbohydrate-rich extracellular material (ECM) during neurulation. Exposure of embryos to this agent for 12 h resulted in failure of closure of the neural tube. Ultrastructural examination revealed an absence of ECM from regions of the neural tube which failed to close.This study was supported by a grant from the National Fund for Research into Crippling Diseases.