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Table 2
Cullin structures and cullin-RING E3 complex assembly
Protein	E3 components			Structures solved*	Key recognition fold on adaptor	Key determinants on cullin NTD

	Adaptor	Substrate recognition	RING

CUL1	Skp1	F-box protein	ROC1/Rbx1	CUL1-Rbx1-Skp1-F box^Skp2[6]; Skp1-Skp2 [60]	Skp1/BTB/POZ fold in Skp1 [6]	CUL1 H2 and H5 helices [6]
CUL2	EloC/EloB	VHL	ROC1/Rbx1	No CUL2 structure; VHL-EloC-EloB [60]	Skp1/BTB/POZ fold in EloC [6,61]	CUL2 H2 and H5 helices [14]
CUL3	BTB (adaptor-targeting)	BTB (adaptor-targeting)	ROC1/Rbx1	SPOP BTB-SBC [13]	BTB [13]; 3-box [13]	CUL3 H2 and H5 helices [62]
CUL4A	DDB1	DCAF	ROC1/Rbx1	DDB1-CUL4A-ROC1 [9]; DDB1-V protein [8]	BPB in DDB1 [9]	CUL4A H2 and H5 helices [9]; CUL4A amino-terminal extension [9]
CUL4B	DDB1	DCAF	ROC1/Rbx1	Not available	BPB in DDB1 (predicted)	CUL4B H2/H5 (predicted)
CUL5	EloC/EloB	SOCS protein	ROC2/Rbx2	CUL5^CTD-Rbx1 [37]; SOCS2- EloC-EloB [63]; HIV Vif-EloC-EloB [16]	Skp1/BTB/POZ fold in EloC [6,61]	CUL5 H2 and H5 helices [64]; CUL5 loop 2 (amino acids 51 to 60) [16]; CUL5 loop 5 (amino acids 118 to 134) [16]
CUL7	Skp1	Fbw8	ROC1/Rbx1	CUL7 CPH-p53 TD [65]	Skp1/BTB/POZ fold in Skp1 (predicted)	Unknown
PARC	Unknown	Unknown	Unknown	Not available	Unknown	Unknown

*Crystal structures of CRL complexes were solved with recombinant human proteins.
Sarikas et al. Genome Biology 2011 12:220 doi:10.1186/gb-2011-12-4-220

Table 2