Specific hydrolysis of methionyl-tRNA Met f catalyzed by a purified peptide.

A peptide initiation factor purified from rat liver and promoting the binding of initiator tRNA and model initiators to 40S and 80S ribosome at an acid pH liberates methionine and N-acetylmethionine from Trna Met f at neutral reaction. Phenylalanyl-tRNA, N-acetylphenylalanyl-tRNA and methionyl-tRNA Met m are not hydrolyzed under the same conditions. Hydrolysis of methionyl-tRNA Met f is stimulated by the presence of the 40S ribosomal subunit and preceeds at 37 degrees C until all the substrate has been split. No hydrolysis of initiator tRNA or N-acetylmethionyl-tRNA Met f occurs at 0 degrees C. Hydrolysis is slightly stimulated by GTP and MG2+ but not by KCl. The binding and hydrolyzing activity associated with a single protein factor may have an important function in regulating the rate of peptide initiation.