Requirement for both the amino-terminal catalytic domain and a noncatalytic domain for in vivo activity of ADP-ribosylation factor GTPase- activating protein

The small GTP-binding protein ADP-ribosylation factor-1 (ARF1) regulates intracellular transport by modulating the interaction of coat proteins with the Golgi complex. Coat protein association with Golgi membranes requires activated, GTP-bound ARF1, whereas GTP hydrolysis catalyzed by an ARF1- directed GTPase-activating protein (GAP) deactivates ARF1 and results in coat protein dissociation. We have recently cloned a Golgi-associated ARF GAP. Overexpression of GAP was found to result in a phenotype that reflects ARF1 deactivation (Aoe, T., Cukierman, E., Lee, A., Cassel, D., Peters, P. J., and Hsu, V. W. (1997) EMBO J. 16, 7305-7316). In this study, we used this phenotype to define domains in GAP that are required for its function in vivo. As expected, mutations in the amino-terminal part of GAP that were previously found to abolish ARF GAP catalytic activity in vitro abrogated ARF1 deactivation in vivo. Significantly, truncations at the carboxyl- terminal part of GAP that did not affect GAP catalytic activity in vitro also diminished ARF1 deactivation. Thus, a non-catalytic domain is required for GAP activity in vivo. This domain may be involved in the targeting of GAP to the Golgi membrane.