GBF1 recruits inactive ARF:GDP complexes to the Golgi (Monetta et al, 2007). There are 5 known ARFs in the human cell. Class I members ARF1 and ARF 3 are expressed at high levels and broadly distributed through the secretory system, while Class II members ARF4 and 5 are expressed at lower levels. ARF6, the single Class III ARF, appears to function more specifically in endocytosis and actin dynamics (Chun et al, 2008; reviewed in D'Souza-Schorey and Chavrier, 2006; Szul and Sztul, 2011). GBF1 has been shown to activate ARF1, 4, and 5, but not ARF3, while single and pairwise knockdown of ARF1, 3, 4 and 5 suggests that no single ARF is responsible for any given step in the secretory pathway (Manolea et al, 2010; Volpicelli-Daley et al, 2005).