Elongation factor 1βγ from Artemia

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Abstract
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.