Members of the regulators of G protein signaling (RGS) family stimulate the intrinsic guanosine triphosphatase (GTPase) activity of the α subunits of certain heterotrimeric guanine nucleotide-binding proteins (G proteins). The guanine nucleotide exchange factor (GEF) for Rho, p115 RhoGEF, has an amino-terminal region with similarity to RGS proteins. Recombinant p115 RhoGEF and a fusion protein containing the amino terminus of p115 had specific activity as GTPase activating proteins toward the α subunits of the G proteins G12 and G13, but not toward members of the G(s), G(i), or G(q) subfamilies of Gα proteins. This GEF may act as an intermediary in the regulation of Rho proteins by G13 and G12.
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