In vitro assays of Arf1 interaction with GGA proteins.

ADP-ribosylation factor 1 (Arf1) is a GTP-binding protein that regulates membrane traffic. This function of Arf1 is, at least in part, mediated by Arf1 x GTP binding to coat proteins such as coatomer, clathrin adaptor protein (AP) complexes 1 and 3, and gamma-adaptin homology-Golgi associated Arf-binding (GGA) proteins. Binding to Arf1 x GTP recruits these coat proteins to membranes, leading to the formation of transport vesicles. Whereas coatomer and the AP complexes are hetero-oligomers, GGAs are single polypeptide chains. Therefore, working with recombinant GGAs is straightforward compared to the other Arf1 effectors. Consequently, the GGAs have been used as a model for studying Arf1 interactions with effectors and as reagents to determine Arf1 x GTP levels in cells. In this chapter, we describe in vitro assays for analysis of GGA interaction with Arf1 x GTP and for determining intracellular Arf1 x GTP levels.