title: CRP-dependent positive autoregulation and proteolytic degradation regulate competence activator Sxy of Escherichia coli.
abstract: Natural competence, the ability of bacteria to take up exogenous DNA and incorporate it into their chromosomes, is in most bacteria a transient phenomenon under complex genetic and environmental control. In the Gram-negative bacteria Haemophilus influenzae and Vibrio cholerae, the master regulator Sxy/TfoX controls competence development. Although not known to be naturally competent, Escherichia coli possesses a Sxy homologue and a competence regulon containing the genes required for DNA uptake. Here, we show that in contrast to other characterised Gamma-proteobacteria, E. coli Sxy is positively autoregulated at the level of transcription by a mechanism that requires cAMP receptor protein (CRP), cyclic AMP (cAMP) and a CRP-S site in the sxy promoter. Similarly, we found no evidence that Sxy expression in E. coli was regulated at the translational level. However, our analysis revealed that Sxy is an unstable protein and that its cellular level is negatively regulated at the post-translational level via degradation by Lon protease. Interestingly, in the Gram-positive model organism Bacillus subtilis, the competence master regulator ComK is also positively autoregulated at the level of transcription and negatively regulated by proteolysis. Together, these findings reveal striking similarities between the competence regulons of a Gram-positive and a Gram-negative bacterium.
authors.affiliation: Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Richardson Road, Newcastle upon Tyne, NE2 4AX, UK.
authors.forename: Milena
authors.initials: M
authors.lastname: Jaskólska
authors.forename: Kenn
authors.initials: K
authors.lastname: Gerdes
mesh_terms: D000242:Cyclic AMP; D002373:Cyclic AMP Receptor Protein / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006706:Homeostasis; D011401:Promoter Regions, Genetic; D049070:Protease La / Q000378:metabolism; D059748:Proteolysis; D018085:Regulon; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism*; D014169:Transformation, Bacterial
chemical_list: D002373:Cyclic AMP Receptor Protein; D029968:Escherichia coli Proteins; C000602560:Sxy protein, E coli; D015534:Trans-Activators; C481662:crp protein, E coli; D000242:Cyclic AMP; C483567:Lon protein, E coli; D049070:Protease La