We are working on the structures of components of the flagellar rod, hook and HAP1-HAP3 junction to understand how these proteins self-assemble in a coordinated manner to create not only extremely stable but also dynamic structures. Clearly it is important that the individual proteins remain monomeric for transport across the cell membranes, but that they bind very tightly once they have reached the target site. In the cell cytoplasm parts of the proteins, notably the N and C termini, appear to be disordered. As a first step to understanding the structure of the hook and rod at the atomic level we are therefore trying to crystallise the more rigid core components of the various proteins which make up these elements of the flagellar motor.