ISOPRENYLATION OF RAB PROTEINS POSSESSING A C-TERMINAL CAAX MOTIF

Rab proteins are small GTPases highly related to the yeast Ypt1 and Se c4 proteins involved in secretion. The Rab proteins were found associa ted with membranes of different compartments along the secretory and e ndocytic pathways. They share distinct C-terminal cysteine motifs requ ired for membrane association. Unlike the other Rab proteins, Rab8, Ra b11 and Rab13 terminate with a C-terminal CaaX motif similar to those of Ras/Rho proteins. This report demonstrates that Rab8 and Rab13 prot eins are isoprenylated in vivo and geranylgeranylated in vitro. Rab11 associates in vitro geranylgeranylpyrophosphate and farnesylpyrophosph ate. Our study shows that the CaaX motif is required for isoprenylatio n.