Both stimulatory and inhibitory GDP GTP exchange proteins, smg GDS and rho GDI, are active on multiple small GTP-binding proteins

Six peaks of small GTP-binding proteins (G proteins) were separated by column chromatographies from the cytosol fraction of the differentiated HL-60 cells: two peaks of rho p21, one peak of smg rap1 p21, two peaks of rac1 p21, and one peak of an unidentified small G protein with a Mr of about 20,000 (20 KG). smg GDS, previously thought to be a stimulatory GDP GTP exchange protein for smg p21, Ki-ras p21, and rho p21, but not for Ha-ras p21 or smg p25A, was also active on rac1 p21. rho GDI, previously thought to be an inhibitory GDP GTP exchange protein specific for rho p21, was also active on rac1 p21. These results indicate that both smg GDS and rho GDI are active on multiple small G proteins.