Coordinate translational regulation in the syntheses of elongation factor 1 alpha and ribosomal proteins in Xenopus laevis.

The regulation of the synthesis of elongation factor 1 alpha (EF-1 alpha) in Xenopus laevis has been analyzed from the point of view of translational control. The 5' end of EF-1 alpha mRNA, examined by primer extension, revealed the presence of a terminal pyrimidine tract that is characteristic of ribosomal protein mRNAs (rp-mRNAs). We have then compared the translation pattern of EF-1 alpha and rp-mRNAs during Xenopus embryogenesis and in Xenopus cultured cells during growth rate changes. In Xenopus embryos EF-1 alpha transcripts, that appear after midblastula transition, are initially mostly localized on mRNP and translationally inactive. Only later in embryogenesis, together with rp-mRNAs, they are gradually recruited on polysomes. Also in Xenopus cells B 3.2, EF-1 alpha mRNA shows a distribution change similar to an rp-mRNA: part of it moves from polysomes to mRNP during serum deprivation and goes back on polysomes after restitution of serum to the culture. Moreover EF-1 alpha mRNA, similarly to rp-mRNAs, is always localized on mRNP or fully loaded on polysomes but never on small polysomes. Therefore EF-1 alpha mRNA for structural features and translation behavior can be included in the 'regulatory' group of rp-mRNAs.