Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complex required for mitotic progression and cytokinesis. The BCR(KLHL42) E3 ubiquitin ligase complex mediates the ubiquitination and subsequent degradation of KATNA1. Involved in microtubule dynamics throughout mitosis. . This is the function of ENSG00000087448 (KLHL42, kelch like family member 42).