Elongation factor 1βγ from Artemia

The guanine nucleotide exchange factor, elongation factor 1βγ (EF‐1βγ) has been purified from Artemia cysts using an improved method. The protein consists of two distinct polypeptides with relative molecular masses of 26000 (EF‐1β) and 46000 (EF‐1γ). A nucleoside diphosphate phosphotransferase activity often found in EF‐1βγ preparations has been completely separated from the actual guanine nucleotide exchange stimulatory activity of EF‐1βγ, thus indicating that nucleotide diphosphate phosphotransferase is not an intrinsic property of EF‐1β. Both EF‐1βγ and EF‐1β have been shown to stimulate the following three reactions to a comparable degree: (a) exchange of GDP bound to EF‐1α with exogenous GDP; (b) EF‐1α‐dependent binding of Phe‐tRNA to ribosomes; (c) poly(U)‐dependent poly(phenylalanine) synthesis. However, a significantly higher nucleotide exchange rate was observed in the presence of EF‐1βγ compared to EF‐1β alone. Concerning elongation factor 1γ (EF‐1γ) the following observations were made. In contrast to EF‐1β, pure EF‐1γ is rather insoluble in aqueous buffers, but the tendency to precipitate can be partially suppressed by the addition of detergents. In particular, EF‐1γ partitions solely into the detergent phase of Triton X‐114 solutions. EF‐1γ is also more susceptible to spontaneous, specific fragmentation. It is remarkably that about 5% of the cellular pool of EF‐1βγ was found to be present in membrane fractions, under conditions where no EF‐1α was detectable in these fractions. Furthermore it was noted that EF‐1βγ copurified strongly with tubulin on DEAE‐cellulose. Moreover, it was observed that from a mixture of EF‐1βγ and tubulin, EF‐1γ coprecipitates with tubulin using a non‐denaturating immunoprecipitation technique. These findings suggest that EF‐1γ has a hydrophobic domain and interacts with membrane and cytoskeleton structures in the cell.