Translation enhancer in the 3′-untranslated region of rotavirus gene 6 mRNA promotes expression of the major capsid protein VP6

Summary.

The eleven rotavirus mRNAs contain 5′-cap structures and most end with the 3′-consensus sequence 5′-UGACC-3′. The UGACC functions as a common translation enhancer (3′-TE-con) that upregulates viral protein expression through a process mediated by the nonstructural protein NSP3. To address the possibility that gene-specific enhancers are also contained in the untranslated regions (UTRs) of the rotavirus mRNAs, we used rabbit reticulocyte lysates to investigate the translation efficiencies of analog RNAs containing viral-specific 5′-and 3′-UTRs and the open reading frame for chloramphenicol acetyltransferase. These experiments combined with the analysis of full-length viral RNAs and RNAs containing 3′-truncations showed that a highly active enhancer was present near the 5′-end of the 139-nucleotide 3′-UTR of the gene 6 mRNA (3′-TEg6). The 3′-TEg6 represents a functionally independent enhancer, as no other portion of the gene 6 mRNA was required for its activity. The 3′-TEg6 differs significantly from the 3′-TE-con in that the gene 6-specific enhancer does not require viral protein for activity and is formed by a sequence unique to only one of the eleven viral mRNAs. Together, our findings suggest that the 3′-UTR of the gene 6 mRNA contains two TEs, one is gene-specific (3′-TEg6) and the other is common to nearly all rotavirus genes (3′-TE-con). The activity of the 3′-TEg6 is likely important for directing the efficient translation of the gene 6 mRNA at levels sufficient to provide the 780 copies of VP6 necessary for the assembly of each progeny virion.