RNASEL and viral infectious disease: To elucidate the roles of the NS4b proteins in the context of viral infection, we inoculated B6 BMM or RNase L−/− BMM with wild-type MHV (MHVWT) or MHV expressing a catalytically inactive NS2 (MHVMut) as well as chimeric MHVMut expressing either WT or mutant MERS-CoV (both full-length and with amino acids 1 to 52 deleted) and BtCoV-SC2013 NS4b proteins (see Fig. 4 for schematics of the chimeric viruses).