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The trafficking of proteins within eukaryotic cells is achieved by the capture of cargo and targeting molecules into vesicles that bud from a donor membrane and deliver their contents to a receiving compartment. This process is bidirectional and may involve multiple organelles within a cell. Distinct coat proteins mediate each budding event, serving both to shape the transport vesicle and to select by direct or indirect interaction the desired set of cargo molecules. Secretion, which has been viewed as a default pathway, may require sorting and packaging signals on transported molecules to ensure their rapid delivery to the cell surface., Eukaryotic cells have an elaborate network of organelles, many of which are in constant and bidirectional communication through a flow of small transport vesicles. For each organelle a specific mechanism [...]

Protein trafficking from the endoplasmic reticulum (ER) to the Golgi apparatus involves specific uptake into coat protein complex II (COPII)-coated vesicles of secretory and of vesicle targeting (v-SNARE) proteins. Here, two ER to Golgi v-SNAREs, Bet1p and Bos1p, were shown to interact specifically with Sar1p, Sec23p, and Sec24p, components of the COPII coat, in a guanine nucleotide-dependent fashion. Other v-SNAREs, Sec22p and Ykt6p, might interact more weakly with the COPII coat or interact indirectly by binding to Bet1p or Bos1p. The data suggest that transmembrane proteins can be taken up into COPII vesicles by direct interactions with the coat proteins and may play a structural role in the assembly of the COPII coat complex., Secretory proteins travel from the ER to the Golgi apparatus in transport vesicles coated with the COPII protein complex (1). The Saccharomyces cerevisiae COPII proteins Sar1p [a small guanosine triphosphatase [...]

A Test of Clathrin Function in Protein Secretion and Cell Growth Coated regions of membranes and coated vesicles have been implicated as intermediates in the vesicle traffic that mediates transport [...]

Clathrin: A Role in the Intracellular Retention of a Golgi Membrane Protein ELABORATION AND MAINTENANCE OF THE COMPARTMENTAL organization of eukaryotic cells requires delivery and retention of components specific for [...]

In this article the authors discuss key evidence for the unconventional secretion of proteins by eukaryotic cells in cell biology research and explore the related questions that remain to be addressed. The authors note that there is some concern among cell biologists that examples of proteins being inefficiently secreted are the result of cell lysis, which is a type of cell death, rather than actual secretion. They add that unconventional secretion may occur via several different pathways and the possible routes for unconventional protein secretion. A diagram illustrating several possible routes of protein secretion, such as direct transit across the plasma membrane without a cell surface transporter, is presented.