The predicted amino acid sequence of a centrosphere protein in dividing sea urchin eggs is similar to elongation factor (EF-1α)

Monoclonal antibody (SU5), prepared from isolated mitotic spindles of sea urchin eggs, stained centro-spheres preferentially and recognized a 50K (K=10³ M_r.) polypeptide on immunoblots. Three positive clones were isolated by screening a λgt11 cDNA expression library prepared from sea urchin egg mRNA with SU5. One clone containing a 1.8-kb (1 kb=10³ base-pairs) insert was selected for further characterization. The β-galactosidase fusion protein encoded by the cDNA clone had an apparent relative molecular mass of 150K, indicating that the inserted cDNA produced an estimated 34K of polypeptide. A single 2.2-kb RNA transcript was detected in sea urchin embryos using the cDNA clone as a probe. The cDNA fragment was sequenced and the nucleotide sequence was used to predict the amino acid sequence of the open reading frames in the clone. The putative gene product shows striking similarity to the peptide chain elongation factor (EF-1α) from yeast, fungus, shrimp, insect, mouse and human.