All eukaryotic cells contain a cytoskeleton composed of microtubules, microfilaments and intermediate filaments that provide the cell with mechanical support and a trackway along which motor proteins can move. Until recently bacteria were thought to lack these structures but this was challenged by the discovery of the protein FtsZ, from which microtubules are thought to have evolved. In September 6 Nature Fusinita van den Ent and colleagues at the MRC Laboratory of Molecular Biology, Cambridge, UK show that the bacterial protein MreB has a similar molecular size to actin and is capable of self-assembling into filaments (Nature 2001, 413:39-44).