Translocation of Ki-ras p21 between membrane and cytoplasm by smg GDS.

We have previously shown that smg GDS forms a complex with Ki-ras 4B p21 and thereby stimulates its GDP/GTP exchange reaction. We have shown here that smg GDS inhibits the binding of Ki-ras 4B p21 to membranes and induces the dissociation of prebound Ki-ras 4B p21 from membranes. Moreover, we have found that cotransfection of the smg GDS and Ki-ras 4B p21 cDNAs into COS7 cells increases the ratio of the cytosolic form of ras p21 to the membrane-bound form and the ratio of the GTP-bound form of ras p21 to the GDP-bound form. These results indicate that smg GDS regulates not only the GDP/GTP exchange reaction of Ki-ras 4B p21 but also its translocation between membrane and cytoplasm.