Although most microtubule growth and shrinkage occurs at the plus end, it can also occur at the minus end. Certain proteins sever and break microtubules (e.g. katanin) [1], whilst other proteins control microtubule disassembly by binding to and destabilizing the lattice (e.g. kinesin-13) [2] and promoting GTP hydrolysis on β-tubulin (e.g. Op18/stathmin) [3]. These proteins require molecules such as ATP to provide the energy needed for subunit removal and their activity can be controlled by kinase-mediated phosphorylation.