Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin ligase complex required for The BCR(KLHL8) ubiquitin ligase complex mediates ubiquitination and degradation of RAPSN. Protein modification; protein ubiquitination. Component of the BCR(KLHL8) E3 ubiquitin ligase complex, at least composed of CUL3, KLHL8 and RBX1. Interacts with RAPSN.