Functions as a component of numerous distinct DCX (DDB1-CUL4-X-box) E3 ubiquitin-protein ligase complexes which mediate the ubiquitination and subsequent proteasomal degradation of target proteins. In the DCX complexes, acts as a scaffolding subunit required to stabilize the complex. Protein modification; protein ubiquitination. Component of numerous DCX (DDB1-CUL4-X-box) E3 ubiquitin-protein ligase complexes which consist of a core of DDB1, cullin-4 (CUL4A or CUL4B), DDA1 and RBX1. Belongs to the DDA1 family.