Binding Protein Complex eIF

The authors concluded that the CBP-containing complex therefore constituted a new initiation factor activity (termed eIF-4F) with a unique functional role, which had presumably previously been undetected because it contaminated preparations of eIF-4B and/or elF-3. eIF-4F was shown to promote maximal mRNA binding to the 40 S ribosomal subunit, in addition to eIF-2, eIF-3, eIF-4A, and eIF-4B. Curiously, all factor requirements, including those for eIF-4F were the same for translation of globin mRNA and for STNV RNA, a naturally uncapped mRNA. A possible role of eIF-4F for translation of the latter RNA was not proposed. 

The 46,000-dalton component of eIF-4F was identified in the same report as being identical to eIF-4A, which was purified independently. Both proteins had the same apparent molecular weight and net charge, as indicated by their mobilities in two-dimensional gels. In addition, eIF-4F could replace eIF-4A in the eIF-4B and ATP-dependent crosslinking to oxidized mRNA. 

is the biochemical reason for the inactivation of the CBP complex and the structural dissociation of the polypeptides The 24-CBP appears to remain in infected cells, able to recognize and bind to mRNA cap groups, but no detailed structural analyses of the protein from either uninfected or infected cells have been performed (see above). The 50,000-dalton subunit represents only a subset of the cell s eIF-4A population, and may contain a covalent modification, as evidenced by a small difference in tryptic peptide maps between the polypeptide isolated from the CBP complex and the majority of eIF-4A isolated independently (Fdery et al., 1983). Thus, although total cellular eIF-4A has been reported to be both structurally (Duncan et al., 1983) and functionally (Etchison et al., submitted) identical in poliovirus-infected HeLa cells compared with uninfected cells, the possibility still remains that virus infection affects the subset of elF-4A in the CBP complex. 

The large polypeptide in the CBP complex, p220, is perhaps the most interesting of all. Little is known about this polypeptide, except its described presence in purified preparations of CBP complex. How- 

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