Specific down-regulator of the NEDD8 conjugation system. Recruits NEDD8, UBD, and their conjugates to the proteasome for degradation. Isoform 1 promotes the degradation of NEDD8 more efficiently than isoform 2. . This is the function of NUB1 (negative regulator of ubiquitin like proteins 1, ENSG00000013374).