Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complex required for synaptic transmission (PubMed:19782033). The BCR(KCTD13) E3 ubiquitin ligase complex mediates the ubiquitination of RHOA, leading to its degradation by the proteasome (PubMed:19782033) Degradation of RHOA regulates the actin cytoskeleton and promotes synaptic transmission (By similarity). Mediates also the ubiquitination and degradation of GluN1/GRIN1 to regulate excitatory synaptic transmission and seizure susceptibility (PubMed:37142655). {ECO:0000250|UniProtKB:Q8BGV7, ECO:0000269|PubMed:19782033, ECO:0000269|PubMed:37142655}. This is the function of KCTD13 (potassium channel tetramerization domain containing 13, ENSG00000174943).