Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complex required for synaptic transmission. The BCR(KCTD13) E3 ubiquitin ligase complex mediates the ubiquitination of RHOA, leading to its degradation by the proteasome, thereby regulating the actin cytoskeleton and promoting synaptic transmission. 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. Component of the BCR(KCTD13) E3 ubiquitin ligase complex, at least composed of CUL3, KCTD13/BACURD1 and RBX1. Interacts with RHOA; with a preference for RhoA-GDP. Interacts with POLD2 and PCNA. Interacts with SPRTN. Belongs to the BACURD family.