A New Method for the Purification of Initiation Factor F2 in High Yield, and an Estimation of Stoichiometry in the Binding Reaction

A simple method is described for purifying protein synthesis initiation factor F2 which involves ammonium sulfate fractional precipitation of a 0.5 m NH4Cl wash of the ribosomes, followed by chromatography on cellulose phosphate and then on Sephadex G-200. Cellulose phosphate chromatography is an especially effective method, producing a 36-fold purification. The over-all yield of F2 is 23%, the over-all purification is 115-fold, and the final product shows one band on analytical disc gel electrophoresis. With this preparation it was shown that 1 molecule of F2 could stimulate the binding of up to 7 N-formylmethionyl tRNA molecules to ribosomes. This indicates that F2 is released from the ribosome after catalyzing the binding reaction and can then be reused.