FIGURE 10.

CIF alters CRL neddylation dynamics. A, CRLs typically cycle between active and inactive states, depending on cullin neddylation status. The NEDD8 system is responsible for the conjugation of NEDD8 to cullins, whereas the CSN juxtaposes this to provide the requisite homeostasis of activated CRLs. B, CIF deamidates NEDD8 attached to cullins (Fig. 7). This results in direct CRL inactivation because CRLs modified with NEDD8 Q40E are not active in vitro (25, 26) and do not support growth in yeast (Fig. 9). The CSN removes NEDD8 Q40E more efficiently than wild-type NEDD8 from CRLs, resulting in an increase in deneddylated CRLs (Fig. 6). Once removed, NEDD8 Q40E is competent for further rounds of CRL modification (Fig. 8). However, the enhanced deneddylation of deamidated NEDD8 results in reduced steady-state levels of neddylated CRLs (Fig. 4), rendering cells incompetent for vegetative growth (Fig. 3).