Fig. 4: Disruption of the oligomerization interfaces influences CUL9–RBX1’s hexameric state and ubiquitylation activity.
a, Schematic of structures highlighting interfaces mediating oligomerization and how their disruption would yield dimeric or monomeric CUL9–RBX1 species. The top shows a cryo-EM map of CUL9–RBX1 hexamer with close-ups of the ARM1 dimer interface and the bridging helix–CR3 interactions at the cullin dimer interface. Each interface is present three times in the CUL9–RBX1 hexamer. The bottom shows ARM1 dimer, monomer and cullin dimer maps dissected from EM density over CUL9–RBX1 hexamer. ARM1 dimer was made by replacing residues 1650–1690 with GSGSGSGS, cullin dimer by the two point mutations (R125A Y152A) and monomer by a combination of both. b, Size-exclusion chromatography analysis of recombinant CUL9–RBX1 and indicated CUL9–RBX1 variants. c, Ubiquitylation assays testing fluorescent ubiquitin (*Ub) transfer to TP53 by indicated CUL9–RBX1 variants (n = 2 technically independent experiments).
