The DET1-DDB1-DDA1 (DDD) complex is a substrate adaptor for transcription factor ubiquitination. In humans, the complex is implicated in ubiquitinating transcription factors that control differentiation of metabolic and immune cells, while in plants it is a key regulator of light-dependent development. The DDD complex associates with the Rbx1-Cullin-4 ubiquitin ligase (CRL4DET1), but also binds a second ubiquitin ligase (COP1) to regulate ubiquitination of some substrates. Using a combination of structural biology and biochemistry we are characterising the functional architecture of DET1 complexes. The cryo-EM structure of the human DDD complex reveals that DET1 contains a specific adaptation for recruiting Ube2e family ubiquitin conjugating enzymes. Further studies suggest that COP1 is recruited to DET1 at a site adjacent to this E2-binding site. I will discuss our current working model for how this multilayered arranegment of substrate adaptors and ligase enzymes work in concert to control ubiquitination of predominantly dimeric transcription factors.