Protein chain initiation in wheat embryo. Resolution and function of the soluble factors.

The complete resolution of the initiation and transfer factors of wheat embryo supernatant is described. Two factors function in chain initiation, as ascertained by (a) their requirement for the formation of a ribosome-messenger RNA complex whose capacity for ammo acid incorporation is insensitive to aurintricarboxylic acid; and (b) their participation in the tobacco mosaic virus RNA-dependent binding of methionyl transfer RNA to ribosomes. The remaining factors, Tl(E) and TZ(E), catalyze the poly(U)-dependent polymerization of phenylalanine, establishing their function primarily in chain elongation. All four factors are required for tobacco mosaic virus RNA-dependent amino acid incorporation.