The ADP-ribosylation factor (ARF) subfamily of small GTPases regulates intr
acellular transport. Although much is known about how ARF1 regulates transp
ort in the secretory pathways, regulation of the endocytic pathways by ARF6
remains less understood. In particular, whereas cycling of ARF1 between me
mbrane and cytosol represents a major mechanism of regulating its function,
this regulation has been questioned for ARF6, In this study, we found that
ARF6 is distributed both on membranes and in the cytosol, Cytosolic ARF6 i
s recruited to membranes in a GTP-dependent manner that is fundamentally si
milar to ARF1. However, unlike ARF1, release of membrane-bound ARF6 to the
cytosol requires hydrolysis of GTP that is sensitive to the level of magnes
ium, These findings suggest that the GTPase cycle of ARF6 also regulates it
s distribution between membrane and cytosol and that this form of regulatio
n will also likely be important for the function of ARF6. Moreover, as ARF6
has little intrinsic ability to hydrolyze GTP, magnesium concentration mos
t likely affects the release of membrane-bound ARF6 by altering the activit
y of its GTPase-activating protein.