Walch-Solimena C, Collins R N, Novick P J
Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
J Cell Biol. 1997 Jun 30;137(7):1495-509. doi: 10.1083/jcb.137.7.1495.
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.
小GTP酶Sec4p是酵母分泌高尔基体后阶段囊泡运输所必需的。我们在此提供证据表明，SEC2（其本身是一个在分泌途径同一阶段起作用的必需基因）中的突变会导致Sec4p错误定位，这是由于囊泡随机而非极化积累所致。Sec2p和Sec4p直接相互作用，Sec4p的无核苷酸构象是与Sec2p相互作用的首选状态。Sec2p作为一种交换蛋白，催化GDP从Sec4上解离并促进GTP的结合。我们提出，Sec2p的功能是将Sec4p的激活与囊泡向胞吐部位的极化递送相偶联。
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