May act as a substrate-specific adapter of an E3 ubiquitin-protein ligase complex (CUL3-RBX1-BTB) which mediates the ubiquitination and subsequent proteasomal degradation of target proteins. Protein modification; protein ubiquitination. Homodimer. Interacts with CUL3A and CUL3B. The BTB/POZ domain mediates the interaction with some component of ubiquitin ligase complexes.