Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin ligase complex that acts as a regulator of neural crest specification (By similarity). The BCR(KBTBD8) complex acts by mediating monoubiquitination of target proteins (By similarity). Component of the BCR(KBTBD8) E3 ubiquitin ligase complex. Translocates to the spindle apparatus during mitosis. Belongs to the KBTBD8 family.