(C) Quantification of Arf6 activity (GTP-Arf6) in HeLa cells transfected to produce either mCherry and Arf6-HA or mCherry-BspF and Arf6-HA by G-LISA. Data are means ± SD of n=3 independent experiments, normalized to mCherry-producing controls. The asterisk indicates a statistically significant difference (P = 0.0026, unpaired Student's t test) between BspF-producing and control conditions. 