How do chromosomes bi-orient on the mitotic spindle?
Our recent data suggest that sister centromeres temporarily attach to microtubules from the same spindle pole (mono-orientation). We discovered that the yeast orthologue of the Aurora B-INCENP protein kinase complex, known as Ipl1-Sli15, is necessary to correct mono-orientation to bi-orientation (ref 5). To promote bi-orientation, centromere-spindle pole connections must be re-oriented if tension is not exerted on the connections. The Ipl1-Sli15 kinase complex facilitates this re-orientation until traction of sister centromeres towards opposite spindle poles creates tension in the surrounding chromatin. We therefore propose that Ipl1-Sli15 is a crucial component of an error-correcting mechanism that promotes bi-orientation.