A four-nucleotide translation enhancer in the 3 '-terminal consensus sequence of the nonpolyadenylated mRNAs of rotavirus

The 5' cap and poly(A) tail of eukaryotic mRNAs work synergistically to enh ance translation through a process that requires interaction of the cap-ass ociated eukaryotic initiation factor, elF-4G, and the poly(A)-binding prote in, PABP. Because the mRNAs of rotavirus, and other members of the Reovirid ae, contain caps but lack poly(A) tails, their translation may be enhanced through a unique mechanism. To identify translation enhancement elements in the viral mRNAs that stimulate translation in vivo, chimeric RNAs were pre pared that contained an open reading frame for luciferase and the 5' and 3' untranslated regions (UTRs) of a rotavirus mRNA or of a nonviral mRNA. Tra nsfection of the chimeric RNAs into rotavirus-infected cells showed that th e viral 3' UTR contained a translation-enhancement element that promoted ge ne expression. The element did not enhance gene expression In uninfected ce lls and did not affect the stability of the RNAs. Mutagenesis showed that t he conserved sequence GACC located at the 3' end of rotavirus mRNAs operate d as an enhancement element. The 3'-GACC element stimulated protein express ion independently of the sequence of the 5' UTR, although efficient express ion required the RNA to contain a cap. The results indicate that the expres sion of viral proteins in rotavirus-infected cells is specifically up-regul ated by the activity of a novel 4-nt 3' translation enhancer (TE) common to the 11 nonpolyadenylated mRNAs of the virus. The 4-nt sequence of the rota virus 3' TE represents by far the shortest of any of the sequence enhancers known to stimulate translation.