Rab1 is an essential regulator of ER to Golgi transport and
participates in traffic events at the donor and acceptor membranes
through its interaction with effectors. A dominant negative Rab1
mutant (Rab1N121I) inhibits sorting of cargo proteins into ER exit
sites (ERES) suggesting that Rab1 modulates cargo sorting. COPII
protein complex (Sar1GTPase, Sec23/24 and Sec13/31) is required
for sorting and concentration of cargo into ERES. To test if COPII
components act as Rab1 effectors we performed GST-pull down
assays using Rab1GTP and rat liver cytosol. Analysis of the
bounded proteins indicates that Rab1, in its active form (Rab1Q67L),
interacts with Sec23. In agreement, double immunofluorescence
assay showed that Rab1Q67L colocalized with COPII structures.
Furthermore, FRAP experiments performed in HeLa cells coexpressing
GFP-Sec13 and Rab1Q67L indicate that Rab1 activity
affects Sec13 membrane association-dissociation kinetics at the
ERES.
These data show that Rab1 interacts with a COPII component,
modulates COPII membrane association dynamic and strongly
suggest that Rab1 activity modulates COPII sorting function at
ERES interfaces