Structural Basis for Subst rate Selectivity of the E 3 Ligase COP 1 Graphical Abstract Highlights

In Brief COP1 proteins are E3 ubiquitin ligases that regulate phototropism in plants and target transcription factors for degradation in mammals. The substratebinding region of COP1 resides within a WD40-repeat domain that also binds to Trib proteins, the adaptors for C/EBPa degradation. Uljon et al. identify the structural basis and key interactions for motif recognition by COP1, and hint at how Trib1 autoinhibition is overcome to target C/EBPa for degradation.