The Cullin-4 Complex DCDC Does Not Require E3 Ubiquitin Ligase Elements To Control Heterochromatin in Neurospora crassa

The cullin-4 (CUL4) complex DCDC (DIM-5/-7/-9/CUL4/DDB1 complex) is essential for DNA methylation and heterochromatin formation in Neurospora crassa. Cullins form the scaffold of cullin-RING E3 ubiquitin ligases (CRLs) and are modified by the covalent attachment of NEDD8, a ubiquitin-like protein that regulates the stability and activity of CRLs. We report that neddylation is not required for CUL4-dependent DNA methylation or heterochromatin formation but is required for the DNA repair functions. Moreover, the RING domain protein RBX1 and a segment of the CUL4 C terminus that normally interacts with RBX1, the E2 ligase, CAND1, and CSN are dispensable for DNA methylation and heterochromatin formation by DCDC. Our study provides evidence for the noncanonical functions of core CRL components.