Ruth S. Perez-Alfaro Moises Santillan Edgardo Galan-Vasquez Agustino Martinez-Antonio Departamento de Ingenieria Genetica, Centro de Investigacion y de Estudios Avanzados del IPN, Unidad Irapuato, Km. 9.6 Libramiento Norte Carr. Irapuato-Leon 36821 Irapuato, Guanajuato, Mexico Centro de Investigacion y de Estudios Avanzados del IPN, Unidad Monterrey, Via del Conocimiento 201, 66600 Apodaca NL, Mexico Network Biology ISSN 2220-8879 http://www.iaees.org/publications/journals/nb/online-version.asp 2014 4 3 95 108 International Academy of Ecology and Environmental Sciences Hong Kong 2 May 2014 5 June 2014 1 September 2014 Escherichia coli transcription factors carbon sources hierarchical use In this work we study the preferential use of carbon sources in the bacterium Escherichia coli. To that end we engineered transcriptional fusions of the reporter gene gfpmut2, downstream of transcription-factor promoters, and analyzed their activity under several conditions. The chosen transcription factors are known to regulate catabolic operons associated to the consumption of alternative sugars. The obtained results indicate the following hierarchical order of sugar preference in this bacterium: glucose > arabinose > sorbitol > galactose. Further dynamical results allowed us to conjecture that this hierarchical behavior might be operated by at least the following three regulatory strategies: 1) the coordinated activation of the corresponding operons by the global regulator catabolic repressor protein (CRP), 2) their asymmetrical responses to specific and unspecific sugars and, 3) the architecture of the associated gene regulatory networks. DOI 10.0000/issn-2220-8879-networkbiology-2014-v4-0008 http://www.iaees.org/publications/journals/nb/articles/2014-4(3)/regulatory-switches-for-hierarchical-use-of-carbon-sources.pdf