Members of the Rab family of small GTPases play important roles in membrane
trafficking along the exocytic and endocytic pathways. The Rab subfamily c
onsists of two highly conserved members, Rab11a and Rab11b. Rab11a has been
localized both to the pericentriolar recycling endosome and to the transGo
lgi network and functions in recycling of transferrin. However, the localiz
ation and function of Rab11b are completely unknown. In this study green fl
uorescent protein (G;FP)-tagged Rab11b was used to determine its subcellula
r localization. GFP-Rab11b colocalized with internalized transferrin, and u
sing different mutants of Rabllb, the role of this protein in transferrin u
ptake and recycling was examined. Two of these mutants, Rab11b-Q/L (constit
utively active) and Rab11b-S/N (constitutively inactive), strongly inhibite
d the recycling of transferrin. Interestingly, both of them had no effect o
n transferrin uptake. In contrast, the C-terminally altered mutant Rab11b-D
elta C, which cannot be prenylated and therefore cannot interact with membr
anes, did not interfere with wildtype Rabllb function. From these data we c
oncluded that functional Rabllb is essential for the transport of internali
zed transferrin from the recycling compartment to the plasma membrane, (C)
Academic Press.