The negative regulator of ubiquitin-like protein 1 (NUB1) is composed of 601 residues with a calculated 69.1-kDa molecular mass. It is an interferon-inducible protein and is predominantly localized in the nucleus. The NUB1 message is specifically expressed in adult human testis, ovary, heart, and skeletal muscle tissues and is developmentally down-regulated in mouse embryos. NEDD8 ultimate buster 1 (NUB1) is an interferon (IFN)-inducible protein that downregulates NEDD8 expression and its conjugation system. NUB1 negatively regulates the ubiquitin-like protein Nedd8 as well as neddylated proteins levels through proteasomal degradation. NUB1 interacts with a ubiquitin-like protein NEDD8 to target the NEDD8 monomer and neddylated proteins to the proteasome for degradation. Therefore, NUB1 is thought to be a potent down-regulator of the NEDD8 conjugation system.