Site-Directed Mutagenesis of Elongation Factor Tu

Abstract

Elongation factor Tu (EF-Tu), a monomeric protein of 393 amino acid residues (M.W. 43,000), is the most abundant protein in E.coli and one of the best studied guanine nucleotide binding proteins, a family of enzymes involved in signal transduction in higher and lower organisms (for references see Bosch et al., 1984; Gilman, 1984; Parmeggiani and Swart, 1985; Bourne, 1986). These proteins bind GTP and GDP, are able to hydrolyze GTP and show typical homologies in their primary structures, especially in the N-terminal 150–200 amino acids. The finding that the ras p21 protein, a mutant variant of which is responsible for oncogenic transformation, is a guanine nucleotide binding protein (Scolnick et al., 1979) further emphasizes the importance of this family. EF-Tu is an essential component of protein biosynthesis, acting as the carrier of aa-tRNA to the ribosome (for references, see Milled: & Weissbach, 1977). As with the other guanine nucleotide binding proteins, GTP induces the active form of the factor: only EF-Tu^·GTP is capable of interacting with aa-tRNA, forming a ternary complex.