Frasnian-Famennian Boundary: Mass Extinctions, Anoxic Oceans, Microtektite Layers, but not much Iridium?

info:eu-repo/semantics/publishe

Geochemistry of the Frasnian-Famennian boundary in Belgium: Mass extinction, anoxic oceans and microtektite layer, but not much iridium?

The Late Devonian, and in particular the Frasnian-Famennian (F/F) boundary, records one of the five largest mass extinctions in the fossil record. Glassy spherules believed to be of impact origin are associated with the F/F boundary in two Belgian sections (Senzeille and Hony). They have also been reported in sediments deposited approximately 1.5 to 2 m.y. above the boundary in south China, and in the Canning Basin (Australia) this event coincides with a 300 pg/g Ir anomaly. In this study, the F/F boundary in the Hony section was analyzed for trace and major elements to test the possibility of an Ir anomaly associated with the spherule layer. No significant positive Ir anomaly was detected in the 2 m of section investigated. Nevertheless, chalcophile elements show an increase within the dark shale bed marking the F/F boundary. This increase is interpreted to represent a reduction in oxygen concentrations in the depo-sitional environment. This level must be equivalent to the upper part of the Kellwasser anoxic event recognized throughout the paleo-Tethys in what is now western Europe. The F/F boundary seems to be marked by a succession of major events, including impact, oxygen-depleted water on the shelf, and worldwide extinction of organisms.SCOPUS: ar.kinfo:eu-repo/semantics/publishe

Emp47p and Its Close Homolog Emp46p Have a Tyrosine-containing Endoplasmic Reticulum Exit Signal and Function in Glycoprotein Secretion in Saccharomyces cerevisiae

The yeast open reading frame YLR080w/EMP46 encodes a homolog of the Golgi protein Emp47p. These two proteins are 45% identical and have a single transmembrane domain in their C-terminal regions and a carbohydrate recognition domain signature in the N-terminal region. The C-terminal tail of Emp46p includes a dilysine signal. This protein is localized to Golgi membranes at steady state by subcellular fractionation and green fluorescent protein labeling. On block of forward transport in sec12-4 cells, redistribution of Emp46p from the Golgi to the endoplasmic reticulum is observed. These localization features are similar to those previously reported for Emp47p. In addition, mutagenesis of the C-terminal region identified a tyrosine-containing motif as a critical determinant of the Golgi-localization and interaction with both COPI and COPII components. Similar motifs are also observed in the C-terminal tail of Emp47p and other mammalian homologs. Disruption of Emp47p displays a growth defect at a high temperature or on Ca(2+)-containing medium, which is rescued by overexpression of Emp46p, suggesting a partially overlapping function between Emp46p and Emp47p. In addition, we found that the disruption of both Emp46p and Emp47p show a marked defect in the secretion of a subset of glycoproteins. Analysis of the C-terminal mutants for Ca(2+) sensitivity revealed that the forward transport of Emp46/47p is essential for their function, whereas the retrograde transport is not. We propose that Emp46p and Emp47p are required for the export of specific glycoprotein cargo from the endoplasmic reticulum