Composition and properties of trypsin-cleaved elongation factor Tu.

Native elongation factor Tu from Escherichia coli, EF-Tu, is initially attacked by trypsin at three adjacent sites in the primary structure. These are arginine-44, arginine-58, and lysine-56. The rates of hydrolysis at the two arginine residues are about the same but that at the lysine residue is much slower. The products of the tryptic digestion have been analysed by Edman degradation and polyacrylamide gel electrophoresis. The peptide from alanine-45 to arginine-58 is eventually excised and does not complex with the remaining polypeptides (fragments A and D). The loss of this peptide does not lead to a concomitant loss of activity in stimulating polyphenylalanine synthesis. The latter is closely correlated with the further hydrolysis of the remaining fragment (A + D) complex. This complex resembles native EF-Tu in its ability to stimulate both polyphenylalanine synthesis and the binding of aminoacyl-tRNA to 70-S ribosomes, but does not form so stable a ternary complex with aminoacyl-tRNA and GTP as the native protein.