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. Interacts with CUL3; interaction is direct and forms a 5:5 heterodecamer (By similarity). 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 (By similarity). Associated with the tectonic-like complex (also named B9 complex); however as Kctd10 has not been identified in all tectonic-like complexes purifications it is unclear whether it is really part of the complex (PubMed:22179047). Belongs to the BACURD family.