Appendix A  Supplementary data
Supplementary material
Transcriptional cross-regulatory network analysed in this study, FFL motifs identified in the network, mRNA abundances and conservation of transcription factors are available in a supplementary excel file.

Acknowledgements
We thank Heladia Salgado and the RegulonDB team for compiling and providing E. coli TF network data. Part of this work is a result of discussions among the three authors at the workshop “Dynamics of Regulatory Networks II” held in 2007 at the Centro Internacional de Ciencias A.C, Cuernavaca, Mexico. Appendix A  Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jmb.2008.05.054