FIGURE 18-42 CPC regulation of microtubule-kinetochore attachment. The Ndc80 complex forms a critical and regulated attachment between the kinetochore and microtubule (+) end. (a) Diagram showing the sleevelike arrangement of the Ndc80 complex linking the inner kinetochore to the (+) end of a microtubule embedded in the outer kinetochore. See S. Santaguida and A. Musacchio, 2009, EMBO J. 28:2511–2531. (b) Diagram of the relationship between the chromosomal passenger complex (CPC), which is associated with the inner kinetochore and contains the kinase Aurora B, and the outer kinetochore, where the phosphatase PP1 binds. Notice that when both kinetochores are under tension, the outer kinetochores move away from the CPC; as a result, Aurora B cannot phosphorylate components in the outer kinetochore, which include the microtubule-binding site of the Ndc80 complex. (c) Cell in metaphase stained for tubulin (red), DNA (blue), Aurora B kinase (green), and the outer kinetochore (magenta). Notice how the outer kinetochore is pulled away from Aurora B (inset).

[Part (c) reprinted by permission from Macmillan Publishers Ltd: from Ruchaud S. et al., “Chromosomal passengers: conducting cell division,” Nature Reviews Molecular Cell Biology, 2007, 8:798–812.]