Long-distance kissing loop interactions between a 3' proximal Y-shaped structure and apical loops of 5' hairpins enhance translation of Saguaro cactus virus.

Circularization of cellular mRNAs is a key event prior to translation initiation. We report that efficient translation of Saguaro cactus virus (SCV) requires a 3′ translational enhancer (PTE) located partially in coding sequences. Unlike a similar PTE reported in the 3′ UTR of Pea enation mosaic virus that does not engage in an RNA:RNA interaction (Wang Z. et al., J. Biol. Chem. 284, 14189–14202, 2009), the SCV PTE participates in long distance RNA:RNA interactions with hairpins located in the p26 ORF and in the 5′ UTR of one subgenomic RNA. At least two additional RNA:RNA interactions are also present, one of which involves the p26 initiation codon. Similar PTE can be found in six additional carmoviruses that can putatively form long-distance interactions with 5′ hairpins located in comparable positions.