Plays a role in the inhibition of host NF-kappa-B activation. Interacts with host BTRC and thereby diminishes ubiquitination of NF-kappa-B inhibitor alpha/NFKBIA. This stabilizes NFKBIA and its interaction with NF-kappaB, so retaining p65/RELA in the cytoplasm and preventing NF-kappa-B-dependent gene expression. Interacts with host BTRC; this interaction inhibits NF-kappa-B activation. Belongs to the poxviridae A49 protein family.