Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin ligase complex that acts as a negative regulator of Wnt signaling pathway and ER-Golgi transport. The BCR(KLHL12) complex is involved in ER-Golgi transport by regulating the size of COPII coats, thereby playing a key role in collagen export, which is required for embryonic stem (ES) cells division: BCR(KLHL12) acts by mediating monoubiquitination of SEC31 (SEC31A or SEC31B). The BCR(KLHL12) complex is also involved in neural crest specification: in response to cytosolic calcium increase, interacts with the heterodimer formed with PEF1 and PDCD6/ALG-2, leading to bridge together the BCR(KLHL12) complex and SEC31 (SEC31A or SEC31B), promoting monoubiquitination of SEC31 and subsequent collagen export. As part of the BCR(KLHL12) complex, also acts as a negative regulator of the Wnt signaling pathway by mediating ubiquitination and subsequent proteolysis of DVL3. The BCR(KLHL12) complex also mediates polyubiquitination of DRD4 and PEF1, without leading to degradation of these proteins. Protein modification; protein ubiquitination. Component of the BCR(KLHL12) E3 ubiquitin ligase complex, at least composed of CUL3 and KLHL12 and RBX1. This complex interacts with DVL3 upon activation of the Wnt signaling pathway by WNT3A. Interacts with DRD4, KLHL2 and SEC31A. Interacts with PEF1 and PDCD6/ALG-2; interaction takes place in response to cytosolic calcium increase and leads to bridge together the BCR(KLHL12) complex and SEC31 (SEC31A or SEC31B). The BTB domain is required for interaction with CUL3. Ubiquitinated by the SCF(FBXL17) complex, leading to its degradation by the proteasome: ubiquitination by the SCF(FBXL17) complex takes place when aberrant BTB domain dimers are formed.