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

The stability of loop-loop kissing interactions in mitochondrial transfer RNA (31) and viral RNA (32, 33) are highly dependent on cation concentration. To test whether SARS S3L2 dimer formation is favored in the presence of Mg 2+ -ions (34), [ 32 P] 5 0 -end-labeled transcripts were incubated in the absence or presence of MgCl 2 at 37 C and separated by native PAGE. Comparison of Figures 4A and B shows that S3L2 self-association is a Mg 2+ -dependent event. In the absence of Mg 2+ , no appreciable change in dimer population was observed between 0 and 48 h at 37 C ( Figure 4A ). Next, we investigated S3L2 self-association as a function of increasing monovalent potassium cation concentration ( Figure 4E ). We found that S3L2 self-association was predominantly driven by the presence of Mg 2+ because significant but slow dimerization resulted from the addition of 6-250 mM KCl in the absence of Mg 2+ ( Figure 4E , open circles), while responses to varying KCl concentrations were negligible in the presence of 5 mM Mg 2+ ( Figure 4E , closed circles).