Results showed that significantly more infected cells with NP signals were detected in rgH5N1/PR8-infected bovine cells than those seen in PR8 H1N1-infected respective cells (Fig. 2), indicating that both the HA and NA genes from the clade 2.3.4.4b H5N1 virus, not six internal genes from the PR8 H1N1 virus, are crucial for rgH5N1/PR8 effective infection and replication in bovine cells. This evidence concerns the gene XK and infection.