Ellen (Yen Kang) France

All eukaryotic cells depend upon efficient mechanisms to direct intracellular traffic of vesicle carriers in order to maintain the functional identity of each compartment essential for viability. At the core of post-Golgi vesicle trafficking is Sec4p, a founding member of the small Rab GTPase family. As a master regulator, Sec4p is thought to interact with multiple effectors to coordinate downstream events and to impart specificity to membrane trafficking at the levels of vesicle transport, docking and fusion to the plasma membrane. To explain the specificity conferred by Sec4p in the docking stage, it is hypothesized that Sec4p may trigger the assembly of the docking complex at specific sites of secretion. The most logical approach to probe the molecular mechanism of Sec4p function is to identify the effectors involved in docking and to characterize their functions. Presently, Sec15p is the only known effector that preferentially binds to GTP-bound Sec4p on the vesicle. The primary emphasis of my work is to characterize Sec15p interactions with the vesicle, which may be crucial for the function of Sec15p.

Previous work has indicated that Sec15p is a good candidate for the Sec4p effector involved at the docking stage.--Sec15p not only physically interacts with activated Sec4p, but is also a member of the Exocyst, a putative membrane tethering complex specific to the post-Golgi secretory pathway. What is the significance of Sec15p associating with vesicles, Sec4p and the tethering complex? Our hypothesis is that Sec15p assumes an active roll in regulating the Exocyst complex assembly at the exocytic sites as a Rab effector and then docks the Sec4p bound vesicle at these sites as a part of the tethering complex. Consequently, Sec15p may be a core component in providing the functional link between Rab GTPase signaling and the specificity of vesicle targeting. In order for Sec15p to play this proposed roll, it must associate with vesicles. Our preliminary data suggests that Sec15p does associate with vesicles and that the association is unlikely to be mediated by its affinity to Sec4p. However, little is known about how Sec15p binding to vesicles is mediated.

Last Updated 20-Dec-2002 Created by Ralph France jmail@bobgoyangi.gcsu.edu

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