Figure 1.

Comparison between the modular SCF and VEC complexes. SCF complex is composed of Skp1, Cdc53, Rbx1, and an F-box protein. Substrate specificity is conferred by the F-box protein. For example, SCF^Skp2 in concert with E2 ubiquitin-conjugating enzyme Cdc34 selectively targets the phosphorylated p27, as well as E2F-1 and Cyclin E, for ubiquitination. VEC complex is composed of Skp1-like elongin C, Cdc53 homologue Cul2, common Rbx1, ubiquitin-like elongin B and an F-box protein pVHL. The SCF-like VEC complex in concert with a cognate E2 targets prolyl hydroxylated HIFα subunits for ubiquitylation. NEDD8 conjugation to Cul1 or Cul2 enhances the E3 activity of both SCF and VEC complexes. Replacement of the F-box protein pVHL with SOCS1 forms SEC that specifically targets VAV or Tel-Jak. B represents elongin B; C represents elongin C; S represents Skp1; R represents Rbx1; N represents NEDD8.