Rbx1 (also designated ROC1 and Hrt1) and the closely related protein Rbx2 (also designated ROC2) are RING finger containing homologs of the yeast protein APC11, a member of the anaphase-promoting complex (APC). Rbx1 was shown to be a component of the von Hippel-Lindau (VHL) transcription elongation complex, which includes VHL, Elongin B, Elongin C and Cullin-2. Rbx1 interacts with Cullin-1 in the SCF (Skp1-Cdc53-F-box protein) ubiquitin ligase complex (2-4). Rbx1 functions as a common subunit of SCF complexes required for ubiquination of various proteins including yeast G1 cyclins, IkBa and b-catenin (2-4). Rbx1 was shown to enhance the ubiquitin ligase activity of the VHL/Cullin-2 complex, and of the SCF/Cullin-1 complex.