Models that depend on Ypt/Rab GTPases were proposed for the maturation of the two sorting compartments of the cell, endosome and Golgi. a) Endosome maturation was observed as Rab5-to-Rab7 conversion, which is dependent on recruitment of Rab5 effectors that act as positive switches for Rab7 recruitment. b) A model was proposed for keeping only one Ypt active at the trans-Golgi. In this model, Ypt32, which functions at the trans-Golgi, recruits a GAP that serves as a negative switch for the cis-Golgi Ypt, Ypt1. The consequence of this recruitment is that Ypt32 would be the only Ypt active in the late Golgi (see text for details). Arrows depict recruitment or activation; flat arrows represent displacement or inhibition.