Selective Recruitment of an E 2 Ubiquitin Complex by an E 3 Ubiquitin Ligase

Background: Rbx1/ROC1 is an E3 ligase adaptor protein that functions with the E2 enzyme CDC34. Results: NMR and biochemical data show that Rbx1/ROC1 binds CDC34 ubiquitin 50-fold tighter than CDC34. Conclusion: Rbx1/ROC1 selectively recruits E2 ubiquitin and releases the E2 after ubiquitin transfer. Significance: Direct evidence is shown for preferential recognition of an E2 ubiquitin complex by an E3 ligase.