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. Author manuscript; available in PMC: 2013 Jul 12.
Published in final edited form as: Physiol Rev. 2011 Jan;91(1):119–149. doi: 10.1152/physrev.00059.2009

FIG. 4.

FIG. 4

The Rab GEF and GAP cascade. Once RabA inserts into its target membrane, it is activated by its respective GEF (step 1). Activated RabA recruits the GEF for the downstream Rab in the pathway RabB (step 2). GTP-bound RabB performs two functions: it recruits the GAP to inactivate RabA (step 3) as well as the GEF for the downstream Rab, RabC (step 4). Activated RabC now recruits the GAP that inactivates RabB (step 5). The concomitant action of GAPs and GEFs ensures the boundaries of each membrane compartment, determined by the actions of their associated Rab, are well-defined.