Sea urchin elongation factor 1δ (EF1δ) and evidence for cell cycle-directed localization changes of a sub-fraction of the protein at M phase

Abstract

Eukaryotic elongation factor 1 (eEF1) is a translational multimolecular complex reported in higher eukaryotes to be a target of CDK1/cyclin B, the universal regulator of M phase, but whose role in the cell cycle remains to be determined. A specific polyclonal antibody was produced and used to characterize the delta subunit of sea urchin elongation factor 1 (SgEF1δ) in early embryos, a powerful model for investigating cell cycle regulation. The SgEF1δ protein was present in unfertilized eggs as two isoforms of 35 and 37 kDa, issued from two different mRNAs. The two canonical eEF1δ partners, eEF1γ and eEF1β, were shown to co-immunoprecipitate with the SgEF1δ isoforms. Both isoforms were associated in a macromolecular complex, which resolved upon gel filtration chromatography at a molecular weight > 400 kDa, suggesting association with other yet unidentified partners. After fertilization, the amount as well as the ratio of both SgEF1δ isoforms remained constant during the first cell division as judged by Western blotting. Immunofluorescence analysis showed that a pool of the protein concentrated as a ring at the embryo nuclear location around the period of nuclear envelope breakdown and was visualized later as two large spheres around the mitotic spindle poles. Thus, the eEF1δ protein shows cell cycle-specific localization changes in sea urchin embryos.