Arabidopsis Sec21p and Sec23p Homologs. Probable Coat Proteins of Plant COP-Coated Vesicles1

Intracellular protein transport between the endoplasmic reticulum (ER) and the Golgi apparatus and within the Golgi apparatus is facilitated by COP (coat protein)-coated vesicles. Their existence in plant cells has not yet been demonstrated, although the GTP-binding proteins required for coat formation have been identified. We have generated antisera against glutathione-S-transferase-fusion proteins prepared with cDNAs encoding the Arabidopsis Sec21p and Sec23p homologs (AtSec21p and AtSec23p, respectively). The former is a constituent of the COPI vesicle coatomer, and the latter is part of the Sec23/24p dimeric complex of the COPII vesicle coat. Cauliflower (Brassica oleracea) inflorescence homogenates were probed with these antibodies and demonstrated the presence of AtSec21p and AtSec23p antigens in both the cytosol and membrane fractions of the cell. The membrane-associated forms of both antigens can be solubilized by treatments typical for extrinsic proteins. The amounts of the cytosolic antigens relative to the membrane-bound forms increase after cold treatment, and the two antigens belong to different protein complexes with molecular sizes comparable to the corresponding nonplant coat proteins. Sucrose-density-gradient centrifugation of microsomal cell membranes from cauliflower suggests that, although AtSec23p seems to be preferentially associated with ER membranes, AtSec21p appears to be bound to both the ER and the Golgi membranes. This could be in agreement with the notion that COPII vesicles are formed at the ER, whereas COPI vesicles can be made by both Golgi and ER membranes. Both AtSec21p and AtSec23p antigens were detected on membranes equilibrating at sucrose densities equivalent to those typical for in vitro-induced COP vesicles from animal and yeast systems. Therefore, a further purification of the putative plant COP vesicles was undertaken.

Interleaflet clear space is reduced in the membrane of COP I and COP II-coated buds/vesicles.

Intracellular transfers between membrane-bound compartments occur through vesicles that bud from a donor compartment to fuse subsequently with an acceptor membrane. We report that the membrane that delimits COP I or COP II-coated buds/vesicles from the endoplasmic reticulum and the Golgi complex has a thinner interleaflet clear space as compared with the surrounding, noncoated parental membrane. This change is compatible with a compositional change of the membrane bilayer during the budding process.

Taking stock after the Warsaw COP. CEPS Commentary, 4 December 2013

Drawing on his direct participation in the latest round of climate talks in Warsaw, Andrei Marcu looks at the results of the 19th COP through the lens of three basic questions, with a view to understanding how much progress was made and where we stand two years ahead of Paris. Are the targets adequate and how do we reach environmentally adequate targets? Can one understand and compare what other Parties are promising to do to ensure that the level of effort is comparable and equitable, and that companies are not asked to do more than their competitors in other jurisdictions? Is there comparability and equity in the eyes of the beholder? Do we understand what tools each country uses (what is available, what one gets as support) to ensure that no one country (and its companies) gets an easier ride or competitive advantage in meeting the commitment/promises that countries make. The author asserts that these questions need to be answered if an agreement is to be reached in 2015. And if they are not, he warns of mistrust, fear of carbon leakage and the temptation to resort to protectionist measures to compensate for competitive disadvantage.

Guide to using School COP to address student discipline and crime problems /

"This guide is a companion to the School COP software package and user manual"--P. 3.