Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complex. The BCR(BACURD3) E3 ubiquitin ligase complex mediates the ubiquitination of target proteins, leading to their degradation by the proteasome (By similarity). Protein modification; protein ubiquitination. Homotetramer; forms a two-fold symmetric tetramer in solution (PubMed:28963344). Interacts with CUL3; interaction is direct and forms a 5:5 heterodecamer (PubMed:28963344). Component of the BCR(BACURD3) E3 ubiquitin ligase complex, at least composed of CUL3, KCTD10/BACURD3 and RBX1 (By similarity). Interacts with DNA polymerase delta subunit 2/POLD2 (By similarity). Interacts with PCNA (PubMed:19125419). Belongs to the BACURD family. Truncated N-terminus. Extended N-terminus.