Figure 9.

NSP2 and σNS employ different mechanisms to promote RNA–RNA interactions. NSP2 (blue) and σNS (green) can bind multiple RNAs per oligomer. NSP2 octamer binding results in efficient RNA unwinding, thereby promoting duplex formation between complementary sequences (highlighted in red and yellow) within interacting genomic segment ssRNAs. In contrast, efficient RNA unwinding by σNS requires a hexamer-to-octamer transition triggered by additional RNA binding. Failure of σNS oligomers to fully disrupt complementary sequences sequestered within RNA secondary structure results in abrogation of strand-annealing activity.