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. Author manuscript; available in PMC: 2011 May 18.
Published in final edited form as: Dev Cell. 2010 May 18;18(5):828–840. doi: 10.1016/j.devcel.2010.03.016

Figure 7. A model for recruitment and regulation of Sec2p by PI4P.

Figure 7

From left to right: Sec2p is initially recruited to the Golgi membrane through the combined signals from PI4P and Ypt32-GTP. The interaction of PI4P with Sec2p also serves to block the binding of Sec15p with Sec2p, thereby facilitating the interaction of Sec2p with Ypt32-GTP. Vesicles bud off of the Golgi carrying Sec2p and Ypt32-GTP, but containing reduced levels of PI4P. Sec2p activates Sec4p, which then recruits its effector, Sec15p. The reduced level of PI4P on the vesicle membrane allows Sec15p to competitively replace Ypt32-GTP on Sec2p. This generates a positive feedback loop in which Sec2p activates Sec4p, Sec4-GTP recruits Sec15p and Sec15p helps retains Sec2p on the vesicle. The elevated levels of Sec4-GTP and Sec15p prepare the vesicle to tether, dock and fuse with the plasma membrane.