Binding of the La autoantigen to the 5 ' untranslated region of a chimerichuman translation elongation factor 1A reporter mRNA inhibits translation in vitro

Human translation elongation factor 1A (EF1A) is a member of a large class of mRNAs, including ribosomal proteins and other translation elongation fac tors, which are coordinately translationally regulated under various condit ions. Each of these mRNAs contains a terminal oligopyrimidine tract (TOP) t hat is required for translational control. A human growth hormone (hGH) exp ression construct containing the promoter region and 5' untranslated region (UTR) of EF1A linked to the hGH coding region (EF1A/hGH) was translational ly repressed following rapamycin treatment in similar fashion to endogenous EF1A in human B lymphocytes. Mutation of two nucleotides in the TOP motif abolished the translational regulation. Gel mobility shift assays showed th at both La protein from human B lymphocyte cytoplasmic extracts as well as purified recombinant La protein specifically bind to an in vitro-synthesize d RNA containing the 5' UTR of EF1A mRNA. Moreover, extracts prepared from rapamycin-treated cells showed increased binding activity to the EF1A 5' UT R RNA, which correlates with TOP mRNA translational repression. In an in vi tro translation system., recombinant La dramatically decreased the expressi on of EF1A/hGH construct mRNA, but not mRNAs lacking an intact TOP element, These results indicate that TOP mRNA translation may be modulated through La binding to the TOP element. (C) 2001 Elsevier Science B.V. All rights re served.