Superposition of the neddylated CRL2FEM1C-Sil1-UBE2R2~ubiquitin-substrate priming structure reported here and the cryo-EM poly-ubiquitin chain extension structure (gray; PDB: 8PQL). Coloring of the subunits in the priming structure is defined inFigure 5A. Donor ubiquitin (UBD) is activated by UBE2R2 for priming of unmodified substrate or chain extension by attachment to acceptor ubiquitin (UBA). The UBE2R2 active sites of the priming and chain extension structures have been noted by stars (yellow and red, respectively). The schematics (right) indicate the regions that were used to perform the structural alignments.
