CYTH2, also known as Cytohesin-2 and ARNO, is an ARF-1 guanine nucleotide exchange factor (GEF). ARF (ADP ribosylation factor) proteins, a group within the RAS superfamily, are GTP-binding proteins central to the process of vesicle budding. This protein promotes guanine-nucleotide exchange on ARF1, ARF3 and ARF6. Also it promotes the activation of ARF factors through replacement of GDP with GTP.