Evidence that the 59-kDa protein synthesis initiation factor from wheat germ is functionally similar to the 80-kDa initiation factor 4B from mammalian cells.

The results of this investigation show that the 59-kDa protein synthesis initiation factor from wheat germ, designated eukaryotic initiation factor (eIF)-4G by Browning et al. (Browning, K.S., Maia, D.M., Lax, S.R., and Ravel, J.M. (1987) J. Biol. Chem. 262, 539-541), cross-links to the 5'-terminal cap of oxidized mRNA in the presence of eIF-4A, eIF-4F, and ATP, stimulates the RNA-dependent ATPase activities of eIF-4A and a mixture of eIF-4A and eIF-4F, and stimulates the unwinding activities of eIF-4A, eIF-4F, and a mixture of eIF-4A and eIF-4F. These findings strongly suggest that the 59-kDa factor from wheat germ is the functional equivalent of the 80-kDa protein synthesis initiation factor, eIF-4B, from mammalian cells. Recent reports indicate that the wheat germ initiation factor which contains two subunits of 80 and 28 kDa and which was given the designation "eIF-4B" by Lax et al. (Lax, S.R., Lauer, S.J., Browning, K. S., and Ravel, J.M. (1986) Methods Enzymol. 118, 109-128) is an isozyme form of eIF-4F and not the functional equivalent of mammalian eIF-4B. On the basis of functional characteristics we propose that the designation for the wheat germ factor containing the 80- and 28-kDa polypeptides be changed from eIF-4B to eIF-(iso)4F and the designation for the 59-kDa factor be changed from eIF-4G to eIF-4B.