Protein chain initiation by methionyl-tRNA

Wheat germ contains three chromatographically distinct methionine tRNA's, of which two species, one major and one minor, appear to function in protein chain initiation as demonstrated by the AUG-dependent reaction with puromycin on wheat germ ribosomes. Wheat germ extracts contain a very active transformylase which formylates the minor methionyl-tRNA. The major initiating methionyl-tRNA is not formylated or otherwise modified by wheat germ extracts. We postulate that protein chain initiation in the cytoplasm of wheat germ can be brought about by the major initiating methionyl-tRNA without prior formylation or other modification of the α amino group.