RNA dimerization plays a role in ribosomal frameshifting of the SARS coronavirus

Ishimaru, Daniella; Plant, Ewan P.; Sims, Amy C.; Yount, Boyd L.; Roth, Braden M.; Eldho, Nadukkudy V.; Pérez-Alvarado, Gabriela C.; Armbruster, David W.; Baric, Ralph S.; Dinman, Jonathan D.; Taylor, Deborah R.; Hennig, Mirko

Most frameshift-stimulating pseudoknots are twostemmed H-type structures. However, we and others have shown that the SARS coronavirus (SARS-CoV) -1 PRF signal is composed of three stems [ Figure 1A ; (1, 2, 6) ]. Secondary structure predictions indicate that the potential to form the third stem is conserved among Group II coronavirus even though the RNA sequences themselves are not well conserved (1) . Interestingly, removal of the third stem from the coronavirus frameshift signal still allows for frameshifting (1, 2, 6, 7) . Thus, it is not clear what the molecular role of the additional stem-loop (Stem 3-Loop 2 [S3L2]) is, and this requires further study.