Eg5 (also called kinesin-like protein 11 or Kif11) belongs to the kinesin-like family of motor proteins important in chromosome positioning, centrosome separation, and mitotic spindle formation. Phosphorylation of Eg5 by mitotic kinases regulates its activity by modulating its association with microtubules. Because anti-mitotic chemotherapeutic drugs, such as taxanes, target microtubules and have pleiotropic and sometimes toxic effects, drugs that target microtubule-associated proteins such as Eg5 are currently in development.