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Polarized secretion requires proper targeting of secretory vesicles to specific sites on the plasma membrane. Here we report that the exocyst complex plays a key role in vesicle targeting. Sec15p, an exocyst component, can associate with secretory vesicles and interact specifically with the rab GTPase, Sec4p, in its GTP-bound form. A chain of(More)
The small GTPase Sec4p is required for vesicular transport at the post-Golgi stage of yeast secretion. Here we present evidence that mutations in SEC2, itself an essential gene that acts at the same stage of the secretory pathway, cause Sec4p to mislocalize as a result of a random rather than a polarized accumulation of vesicles. Sec2p and Sec4p interact(More)
SEC2 is an essential gene required for polarized growth of the yeast Saccharomyces cerevisiae. It encodes a protein of 759 amino acids that functions as a guanine nucleotide exchange factor for the small GTPase Sec4p, a regulator of Golgi to plasma membrane transport. Activation of Sec4p by Sec2p is needed for polarized transport of vesicles to exocytic(More)
After exocytosis, synaptic vesicles rapidly endocytose and recycle but little is known about the molecular mechanisms involved. Rab5 is a ubiquitous low molecular weight GTP-binding protein required for endosomal fusion in fibroblasts. We have now raised polyclonal and monoclonal antibodies to rat Rab5 and show that in rat brain, Rab5 is a major synaptic(More)
Synaptophysins are abundant synaptic vesicle proteins present in two forms: synaptophysin, also referred to as synaptophysin I (abbreviated syp I), and synaptoporin, also referred to as synaptophysin II (abbreviated syp II). In the present study, the properties and localizations of syp I and syp II were investigated to shed light on their relative(More)
Phosphatidylinositol 4-phosphate (PI(4)P) is a key regulator of membrane transport required for the formation of transport carriers from the trans-Golgi network (TGN). The molecular mechanisms of PI(4)P signaling in this process are still poorly understood. In a search for PI(4)P effector molecules, we performed a screen for synthetic lethals in a(More)
Synaptotagmin is known to be a major membrane protein of synaptic vesicles (SVs) in neurons. We have now used an immunoisolation procedure to demonstrate that synaptotagmin is also present in the membranes of peptide containing large dense-core vesicles (LDCVs) of rat hypothalamus and bovine posterior pituitary. Synaptotagmin bead-immunoisolated organelles(More)
Sec2p is required for the polarized transport of secretory vesicles in S. cerevisiae. The Sec2p NH(2) terminus encodes an exchange factor for the Rab protein Sec4p. Sec2p associates with vesicles and in Sec2p COOH-terminal mutants Sec4p and vesicles no longer accumulate at bud tips. Thus, the Sec2p COOH terminus functions in targeting vesicles, however, the(More)
A variety of peptide-secreting endocrine cells contain a population of recycling microvesicles that share several major membrane polypeptides with neuronal synaptic vesicles (SVs). The function of these synaptic-like microvesicles (SLMVs) remains to be elucidated. It was previously suggested that SLMVs of pancreatic beta cells may store and secrete(More)