When a virus enters a host cell it can be sensed by pattern recognition receptors (PRRs) that sensed conserved features of a virus called a pathogen associated molecular pattern (PAMP). For RNA viruses, this is often double stranded RNA, in the form of a replication intermediate or a structured region of the viral genome. Activation of PRRs lead to downstream signaling that induces type I interferons (IFNs) (Fig. 1 A and C) that can then activate the IFN-response pathway (Fig. 1 B) to induces hundreds of IFN-stimulated genes, which can have direct antiviral properties. As innate immunity is the first line of defense against viruses, they have evolved several strategies to evade sensing by the host cell. One mechanism that is commonly used is cleavage of host innate immune proteins by viral proteases. The most well studied is the HCV protease complex, NS3/4A, cleavage of MAVS, an innate immune adaptor protein. There has been limited study of Coronavirus cleavage of host innate immune proteins by the viral protease 3Cysteine-like protease (3CLpro, nsp5). It is known that two porcine coronaviruses use the 3CLpro to cleave NEMO, an NF-kB inhibitor protein, but other host targets have not been studied. Our research focuses on testing whether the coronavirus 3CLpro is involved in innate immune evasion, cleaves predicted host targets within the innate immune pathways, and whether there are host species differences in the ability of 3CLpro to cleave the target protein.