 CUL4A is also modified by covalent attachment of a NEDD8 molecule at a highly conserved lysine residue in the C-terminal region.This modification appears to induce conformational changes which promotes flexibility in the RING domain of cullin proteins and enhanced ubiquitin ligase activity.Overall, CRL4A complexes have a modular structure which allows for sophisticated regulation by the cell and influence over numerous substrates and processes in the cell.