BAG6 and avian influenza: Notably, BAG6 recognizes the N-terminus of PB2 and promotes PB2 ubiquitination at its K189 residue, which is highly conserved among avian and human influenza strains from Global Initiative on Sharing Avian Influenza Data (GISAID, www.epicov.org) (S1 Table), providing the mechanistic basis that BAG6 acts as a potent antiviral factor during both human- and avian-origin IAV infection.