The coordination of flagellar gene expression and the flagellar assembly pathway.

The assembly of a bacterial flagellum requires the coordinated synthesis of over 60 gene products. These genes encode structural and regulatory proteins. A key feature of all flagellar systems is the ability to sense the progression of assembly and the assimilation of this information to allow for the coordination of flagellar gene expression. Our understanding of the regulation of flagellar gene expression encompasses flagellar systems from all corners of the bacterial kingdom. All flagellar systems coordinate flagellar gene expression through a transcriptional hierarchy central to an integrated regulatory network of multiple regulatory components. These networks exhibit a number of conserved circuit architectures reflective of the strong conservation found within the structural components of the flagellum. However, a fascinating level of diversity is evident amongst flagellar systems in how assembly intermediates are sensed and how the perception of these intermediates modulates the activity of the associated transcriptional hierarchy. This chapter explores the conservation and divergence exhibited amongst flagellar system regulatory networks.