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. Author manuscript; available in PMC: 2012 Jul 1.
Published in final edited form as: Trends Cell Biol. 2011 May 6;21(7):383–386. doi: 10.1016/j.tcb.2011.03.006

Figure 3. The Rab cascade model.

Figure 3

(a) In yeast, GTP-bound Ypt32p directly interacts with Sec2p, the GEF for Sec4p. This interaction helps to recruit Sec2p to the secretory vesicles in close proximity to Sec4p for its activation. The GTP-bound Sec4p directly interacts with the exocyst to regulate vesicle tethering at the daughter cell plasma membrane. GTP-Sec4p is later switched to its inactive GDP-bound form by GTP hydrolysis facilitated by its GTPase Activating Proteins (GAPs). (b) In mammalian cells, Rab11, in its GTP-bound form, directly interacts with Rabin8. Rab11 stimulates the GEF activity of Rabin8 towards Rab8 and may also help to recruit Rabin8 to the transport carriers. The activated Rab8 regulates membrane trafficking to the plasma membrane through interaction with its downstream effectors, such as the exocyst. The GTP-bound Rab11 was also shown to interact with the exocyst subunit Sec15. GTP-Rab8 is later switched to its inactive GDP-bound form by GTP hydrolysis facilitated by its GAPs.