The role of FIS protein in the physiological control of the expression of the Escherichia coli meta-hpa operon

10 páginas, 6 figuras, 1 tabla -- PAGS nros. 2151-2160Expression from the Escherichia coli W meta-hpa operon promoter (Pg) is under a strict catabolic repression control mediated by the cAMP-catabolite repression protein (CRP) complex in a glucose-containing medium. The Pg promoter is also activated by the integration host factor (IHF) and repressed by the specific transcriptional regulator HpaR when 4-hydroxyphenylacetate (4HPA) is not present in the medium. Expression from the hpa promoter is also repressed in undefined rich medium such as LB, but the molecular basis of this mechanism is not understood. We present in vitro and in vivo studies to demonstrate the involvement of FIS protein in this catabolic repression. DNase I footprinting experiments show that FIS binds to multiple sites within the Pg promoter. FIS-site I overlaps the CRP-binding site. By using an electromobility shift assay, we demonstrated that FIS efficiently competes with CRP for binding to the Pg promoter, suggesting an antagonist/competitive mechanism. RT-PCR showed that the Pg repression effect is relieved in a FIS deleted strain. The repression role of FIS at Pg was further demonstrated by in vitro transcription assays. These results suggest that FIS contributes to silencing the Pg promoter in the exponential phase of growth in an undefined rich medium when FIS is predominantly expressedThis work was supported by Comunidad Autónoma de Madrid Grant AMB-259-0505, by Comisión Interministerial de Ciencia y Tecnología Grants BIO2007-67304-C02 and CTM2006-04007, by European Union Grants GEN 2006-27750-C5-3-E and NMP2-CT-2007-026515, and by the Programme de Recherche Fondamentale en Microbiologie, Maladies Infectieuses et ParasitairesPeer reviewe