Conserved RNA secondary structure in Cherry virus A 5'-UTR associated with translation regulation.

ABSTRACT

BACKGROUND: A variety of cis-acting RNA elements with structures in the 5'- or 3'-untranslated region (UTR) of viral genomes play key roles in viral translation. Cherry virus A (CVA) is a member of the genus Capillovirus in the family Betaflexiviridae. It has a positive single-stranded RNA genome of ~ 7400 nucleotides (nt). The length of the CVA 5'-UTR is ~ 100 nt; however, the function of this long UTR has not yet been reported. METHODS: Molecular and phylogenetic analyses were performed on 75 CVA sequences, which could be divided into four groups, and the RNA secondary structure was predicted in four CVA 5'-UTR types. These four CVA 5'-UTR types were then inserted upstream of the firefly luciferase reporter gene FLuc (FLuc), and in vitro translation of the corresponding transcripts was evaluated using wheat germ extract (WGE). Then, in-line structure probing was performed to reveal the conserved RNA structures in CVA-5'UTR. RESULTS: The four CVA 5'-UTR types appeared to have a conserved RNA structure, and the FLuc construct containing these four CVA 5'-UTR types increased the translation of FLuc by 2-3 folds, suggesting weak translation enhancement activity. Mutations in CVA 5'-UTR suppressed translation, suggesting that the conserved RNA structure was important for function. CONCLUSION: The conserved RNA secondary structure was identified by structural evolution analysis of different CVA isolates and was found to regulate translation.