Exo1 is a modifier of Golgi ARF1 GTPase activity. Because Exo1 affects a subset of the membrane events that are blocked by BFA, but seems to have a different protein target (and presumably has different side effects), it provides an independent means to interfere with Golgi activity. Exo1 Disrupts Vesicular Traffic from the ER to the Golgi apparatus by disrupting Golgi structures. Exo1 inhibits exocytosis with an IC ₅₀ of ~20 μM. Exo1 prevents acquisition of endoglycosidase H resistance by newly synthesized proteins such as VSVGts-GFP, transferrin, and MHC class I.