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Using a new assay for membrane fusion between late Golgi/endosomal compartments, we have reconstituted a rapid, robust homotypic fusion reaction between membranes containing Kex2p and Ste13p, two enzymes resident in the yeast trans-Golgi network (TGN). Fusion was temperature, ATP, and cytosol dependent. It was inhibited by dilution, [Ca.sup.+2] chelation, N-ethylmaleimide, and detergent. Coimmunoisolation confirmed that the reaction resulted in cointegration of the two enzymes into the same bilayer. Antibody inhibition experiments coupled with antigen competition indicated a requirement for soluble NSF attachment protein receptor (SNARE) proteins Tlg1p, Tlg2p, and Vti1p in this reaction. Membrane fusion also required the rab protein Vps21p. Vps21p was sufficient if present on either the Kex2p or Ste13p membranes alone, indicative of an inherent symmetry in the reaction. These results identify roles for a Tlg SNARE complex composed of TIg1p, TIg2p, Vti1p, and the rab Vps21p in this previously uncharacterized homotypic TGN fusion reaction.

Glycosylphosphatidylinositol (GPI)-anchored membrane proteins of Saccharomyces cerevisiae exist with two types of lipid moiety—diacylglycerol or ceramide—both of which contain 26:0 fatty acids. To understand at which stage of biosynthesis these long-chain fatty acids become incorporated into diacylglycerol anchors, we compared the phosphatidylinositol moieties isolated from myo-[2-3H]inositol­labelled protein anchors and from GPI intermediates. There is no evidence for the presence of long-chain fatty acids in any intermediate of GPI biosynthesis. However, GPI-anchored proteins contain either the phosphatidylinositol moiety characteristic of the precursor lipids or a version with a long-chain fatty acid in the sn-2 position of glycerol. The introduction of long-chain fatty acids into sn-2 occurs in the endoplasmic reticulum (ER) and is independent of the sn-2-specific acyltransferase SLC1. Analysis of ceramide anchors revealed the presence of two types of ceramide, one added in the ER and another more polar molecule which is found only on proteins which have reached the mid Golgi. In summary, the lipid of GPI-anchored proteins can be exchanged by at least three different remodelling pathways: (i) remodelling from diacylglycerol to ceramide in the ER as proposed previously; (ii) remodelling from diacylglycerol to a more hydrophobic diacylglycerol with a long-chain fatty acid in sn-2 in the ER; and (iii) remodelling to a more polar ceramide in the Golgi. [ABSTRACT FROM AUTHOR]

In the Biosphere Reserve of the Maya Lowlands, the large‐scale characterisation of the current wetlands ecology and the exploitation and management of their natural resources by the ancient Maya is severely constrained by the forest. This paper presents an integrated geomatic, geoarchaeological and ecological approach, developed to overcome this obstacle in the microregion of the Naachtun Maya city. It is based on the analysis of LiDAR, and field and laboratory data. This approach has revealed the mosaic of current ecological conditions of the wetlands, thanks to the characterisation and spatial modelling of the landforms, hydrology, vegetation and soil cover. It has enabled the characterisation of numerous hydraulic and agricultural structures: 70 large reservoirs, raised fields (the largest over 1.5 km²), canals and ditches (with a cumulative length of over 300 km) and dikes. Eight morphological types of hybrid structures—hydraulic and agricultural—are described. These constructions have enabled the intensive exploitation of water and soil resources, their management and the resulting environmental risks. This study has shown that the agroecosystems of lowland areas were created as early as ~1500 B.C.E. and evolved in a polyphasic way, until a phase of radical decline around 1000 C.E. This study has made it possible to characterise the legacy of the Maya Early Anthropocene on current wetlands, as well as their important natural and cultural heritage. [ABSTRACT FROM AUTHOR]