The conserved Ypt/Rab GTPases regulate all steps of the intracellular transport pathways. In yeast and human cells, Ypt1/Rab1 regulate early steps of secretion and autophagy, whereas Ypt31/Rab11 regulate a late step in secretion, and the TRAPP complexes act as their activators. The Ypt and transport step specificity of TRAPP complexes is currently controversial. Here, we use in vivo analyses of mutations in subunits of yeast TRAPP complexes to determine these specificities. First, deletion of th