This is consistent with functional studies of SL6 which demonstrate that SL6 is not 540 essential for MHV replication (Yang et al., 2015) , in contrast to structural elements that are 541 entirely within the 5'UTR (SL1, SL2, SL4) or to the trifurcuated SL5 stem-loop which extends 542 from the 5'UTR into the nsp1 coding sequence, which are lethal or result in viruses that are 543