Aurora kinase B is a protein that functions in the attachment of the mitotic spindle to the centromere. The expression and activity of Aurora B are regulated according to the cell cycle. Expression of Aurora B reaches a maximum at the G2-M transition, whereas Aurora B protein is most active during mitosis. The Aurora kinases associate with microtubules during chromosome movement and segregation. Aurora kinase B localizes to microtubules near kinetochores, specifically to the specialized microtubules called K-fibers, and Aurora kinase A localizes to centrosomes. In cancerous cells, over-expression of these enzymes causes unequal distribution of genetic information, creating aneuploid cells, a hallmark of cancer.