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 (By similarity). Protein modification; protein ubiquitination. Component of the BCR(KLHL42) E3 ubiquitin ligase complex, at least composed of CUL3 and KLHL42. Interacts (via the BTB domain) with CUL3. Interacts (via the kelch domains) with KATNA1 (By similarity). Predominantly in mitotic cells. Localized diffusely in the cytoplasm during the interphase. During metaphase is localized throughout the cell and more widely dispersed than the microtubules. In anaphase cells is localized between the two sets of separated chromosomes as well as at the spindle poles (By similarity). During telophase is localized arround the nuclei of the two daughter cells. Not detected at the midbody region during cytokinesis.