Purification, characterization, and possible functions of small molecular weight GTP-binding proteins

GTP-binding proteins with molecular weights of approximately 20,000 are designated small Mr G proteins. We purified four small Mr G proteins to near homogeneity from bovine brain crude membranes. Properties of these proteins, 20K G, 21K G, 22K G, and 24K G, were then assessed. The cDNA of 22K G and 24K G were cloned, and their nucleotide and amino acid sequences were determined. Three types of both C-terminal sequences and amino acid sequences were identified. We conclude that small Mr G proteins and large Mr G proteins are components of large intracellular regulatory and messenger systems with specific roles in cell function regulation.