BUB1 is a serine/threonine-protein kinase that play a central role in mitosis. BUB1 plays a critical role in the mitotic checkpoint, a crucial mechanism that ensures proper chromosome segregation during cell division. BUB1 is located at the kinetochores, the protein structures on chromosomes where spindle fibers attach during mitosis. Such localization allows BUB1 to monitor microtubule attachment to kinetochores, ensuring chromosomes are correctly aligned before cell proceeds to anaphase. When BUB1 detects misalignment or improper attachment, a checkpoint response activates to halt the cell cycle, preventing potential genomic instability and aneuploidy. BUB1′s role in maintaining genomic integrity highlights potential applications in cancer research, where mitotic checkpoint dysregulation can lead to tumorigenesis.