As noted above,  N protein-recruited DDX1 functions in the RTC in facilitating TRS read-through and synthesis of long sgmRNAs. The 3b proteins of IBV and SARS-CoV, though different in nature, have also been located in part in the nuclei of transfected or infected cells. Following nuclear localization, SARS-CoV 3b protein trafficts to the outer membrane of mitochondria, where it inhibits the induction of type 1 interferon (IFN) elicited by RIG-I and the mitochondrial antiviral signaling protein. Similarly, the 4b proteins of MERS-CoV, bat coronavirus (BtCoV)-HKU4, and BtCoV-HKU5 also localize to the nucleus and inhibit type  1 IFN  induction and, less efficiently, NF-kB signaling pathways.