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 (PubMed:15982757). Interacts with PCNA (By similarity). Expressed at highest levels in lung. Also detected in testis and heart. Very low expression, if any, in brain, liver, spleen, kidney and skeletal muscle. By tumor necrosis factor/TNF in cells. Belongs to the BACURD family.