Elongation factor 1β of artemia: Localization of functional sites and homology to elongation factor 1δ

Abstract

Elongation factor (EF)-1β, a 26 kDa protein, is the eukaryotic equivalent of bacterial EF-Ts, the nucleotide exchange factor in protein synthesis. EF-1β catalyzes the exchange of guanine nucleotides bound to EF-1α; the latter protein is the eukaryotic equivalent of bacterial EF-Tu. Limited proteolytic cleavage studies on EF-1β lead to the following picture: the protein is composed of two domains, an aminoterminal and a carboxyterminal domain, connected to each other by a stretch of hydrophilic, charged amino acids situated in the middle of the molecule. The carboxyterminal domain supplies the catalytic site for the nucleotide exchange reaction, whereas the aminoterminal domain interacts with EF-1γ, the third component of elongation factor 1. The regulatory, serine phosphate residue, Ser-89, localized in the hydrophilic stretch of EF-1β, does not appear to be necessary for the basic exchange reaction. The fourth component of the high molecular weight elongation factor complex (EF-1 H), named EF-1δ or 28 K protein, is homologous to EF-1β and contains regions very similar to the carboxyterminal part. EF-1δ was found to be active in the nucleotide exchange reaction.