Resolution of the Polypeptide Chain Elongation Factor-1βγ into Subunits and Some Properties of the Subunits

Polypeptide chain elongation factor-lβγ (EF-1βγ), an eukaryotic counterpart to bacterial EF-Ts, has been purified to a homogeneous state, and shown to have a molecular weight of about 90,000. It consisted of unequal subunits with molecular weights of 30,000 (EF-1β) and 55,000 (EF-1γ) Thus, separation of these subunits was attempted by gel filtration of EF-1βγ treated with guanidine hydrochloride on a column of Sephadex G-200 in the presence of urea. After removing urea by dialysis, the enzymatic activities of the separated subunits were examined by means of the following three reactions, all of which have previously been shown to be stimulated by EF-βγ i) exchange of GDP bound to EF-1γ with exogenous GTP, ii) EF-1α a-dependent binding of Phe-tRNA to ribosomes, and iii) poly(U)-dependent polyphenylalanine synthesis. Under the standard conditions, EF-1β stimulated all of these reactions to the same level as EF-1βγ when the amount of the former was adjusted to be one-third of that of the latter, or the molar concentrations of these factors were the same. This suggests that the effect of EF-1βγ on these reactions could be accounted for that of the EF-1β moiety in the complex. However, when the concentrations of both magnesium acetate and KCI in the reaction mixture were increased, it was observed that EF-1βγ stimulated polyphenylalanine synthesis much more effectively than EF-1βγ The amino acid composition of EF-1β as well as EF-1βγ was determined.