Kinetically distinct sorting pathways through the Golgi exhibit different requirements for Arf1.

To investigate the role of cytoplasmic sequences in directing transmembrane protein trafficking through the Golgi, we analyzed the sorting of VSV tsO45 G fusions with either the native G cytoplasmic domain (G) or an alternative cytoplasmic tail derived from the chicken AE1-4 anion exchanger (G(AE) ). At restrictive temperature G(AE) and G accumulated in the ER, and upon shifting the cells to permissive temperature both proteins folded and underwent transport through the Golgi. However, G(AE) and G did not form hetero-oligomers upon the shift to permissive temperature and they progressed through the Golgi with distinct kinetics. In addition, the transport of G through the proximal Golgi was Arf1 and COPI-dependent, while G(AE) progression through the proximal Golgi was Arf1 and COPI-independent. Although Arf1 did not regulate the sorting of G(AE) in the cis-Golgi, Arf1 did regulate the exit of G(AE) from the TGN. The trafficking of G(AE) through the Golgi was similar to that of the native AE1-4 anion exchanger, in that the progression of both proteins through the proximal Golgi was Arf1-independent, while both required Arf1 to exit the TGN. We propose that the differential recognition of cytosolic signals in membrane-spanning proteins by the Arf1-dependent sorting machinery may influence the rate at which cargo progresses through the Golgi.