The microtubule (MT) cytoskeleton is highly dynamic. Polymerizing and depolymerizing filaments coexist within the same MT population, and this is regulated by a variety of MT-associated proteins and destabilizing factors. MT synthesis also depends on five tubulin-specific chaperones – cofactors A–E – which promote the folding of new tubulin dimers. On , Nicholas Cowan and co-workers describe a novel cofactor-E-related protein – E-like – that has a rather different activity: it promotes MT destruction (see ). They find that overexpressing E-like in HeLa cells completely destroys the MT cytoskeleton. By contrast, suppressing its expression by RNAi increases the number of stable MTs in the cells significantly. The authors go on to show that E-like disrupts tubulin dimers directly and targets them for destruction by the proteasome. Cowan and co-workers also identify a ubiquitin-like (UBL) domain in E-like and suggest that this could be responsible for proteasome targeting. Interestingly, they note that intracellular membranes become clustered around the MT-organizing centre when E-like is suppressed. Since MTs are tracks for vesicle transport, E-like might therefore control membrane trafficking by regulating the overall stability of the MT network.
