Isolation and characterization of factors from wheat germ that exhibit eukaryotic initiation factor 4B activity and overcome 7-methylguanosine 5'-triphosphate inhibition of polypeptide synthesis.

Abstract

Three highly purified preparations (preparations I, II-1, and II-2) were obtained from wheat germ and supported in vitro polypeptide synthesis directed by capped or uncapped mRNA in a eukaryotic initiation factor 4B (eIF-4B)-deficient system. The 3 preparations differ in polypeptide composition and in the ability to overcome the inhibitory effect of 7-methyl-GTP (m7GTP) on in vitro polypeptide synthesis. Preparation I contains 2 polypeptides (MW = 80,000 and 28,000), which are present in a 1:1 molar ratio and are associated in a high MW complex. Preparation II-1 contains 2 major polypeptides (MW = 220,000 and 26,000) and preparation II-2 also contains 2 major polypeptides (MW = 110,000 and 26,000). Preparations II-1 and II-2 are high MW complexes; neither contains detectable amounts of a MW 80,000 or a MW 50,000 component. Preparations II-1 and II-2 both overcome m7GTP inhibition, whereas preparation I does not. These findings raise several questions with regard to the identity of eIF-4B and its relationship to cap recognition factors.