This is the neddylation site of cullin proteins which are afamily of structurally related proteins containing anevolutionarily conserved cullin domain. With the exception ofAPC2, each member of the cullin family is modified by Nedd8 andseveral cullins function in Ubiquitin-dependent proteolysis, aprocess in which the 26S proteasome recognises and subsequentlydegrades a target protein tagged with K48-linked poly-ubiquitinchains. Cullins are molecular scaffolds responsible forassembling the ROC1/Rbx1 RING-based E3 ubiquitin ligases, ofwhich several play a direct role in tumorigenesis. Nedd8/Rub1 isa small ubiquitin-like protein, which was originally found to beconjugated to Cdc53, a cullin component of the SCF(Skp1-Cdc53/CUL1-F-box protein) E3 Ub ligase complex inSaccharomyces cerevisiae, and Nedd8 modification has now emergedas a regulatory pathway of fundamental importance for cell cyclecontrol and for embryogenesis in metazoans. The only identifiedNedd8 substrates are cullins. Neddylation results in covalentconjugation of a Nedd8 moiety onto a conserved cullin lysineresidue [1]. Cullin protein neddylation domain Cullin_Nedd8