Sec2p mediates nucleotide exchange on Sec4p and is involved in polarized delivery of post-Golgi vesicles.
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 directly, with the nucleotide-free conformation of Sec4p being the preferred state for interaction with Sec2p. Sec2p functions as an exchange protein, catalyzing the dissociation of GDP from Sec4 and promoting the binding of GTP. We propose that Sec2p functions to couple the activation of Sec4p to the polarized delivery of vesicles to the site of exocytosis.
Walch-Solimena
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Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Collins
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RN
Novick
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PJ
D000595:Amino Acid Sequence; D001692:Biological Transport / Q000235:genetics; D016764:Cell Polarity; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure*; D020662:Guanine Nucleotide Exchange Factors; D008969:Molecular Sequence Data; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D020691:rab GTP-Binding Proteins
D005656:Fungal Proteins; D020662:Guanine Nucleotide Exchange Factors; C064456:SEC2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D019204:GTP-Binding Proteins; C064320:SEC4 protein, S cerevisiae; D020691:rab GTP-Binding Proteins