title: Mechanism of Antiactivation at the Pseudomonas sp. Strain ADP σN-Dependent PatzT Promoter.
abstract: PatzT is an internal promoter of the atzRSTUVW operon that directs the synthesis of AtzT, AtzU, AtzV, and AtzW, components of an ABC-type cyanuric acid transport system. PatzT is σ(N) dependent, activated by the general nitrogen control regulator NtrC with the assistance of protein integration host factor (IHF), and repressed by the LysR-type transcriptional regulator (LTTR) AtzR. We have used a variety of in vivo and in vitro gene expression and protein-DNA interaction assays to assess the mechanisms underlying AtzR-dependent repression of PatzT Here, we show that repression only occurs when AtzR and NtrC interact simultaneously with the PatzT promoter region, indicating that AtzR acts as an antiactivator to antagonize activation by NtrC. Furthermore, repression requires precise rotational orientation of the AtzR and NtrC binding sites, strongly suggesting protein-protein interaction between the two proteins on the promoter region. Further exploration of the antiactivation mechanism showed that although AtzR-dependent repression occurs prior to open complex formation, AtzR does not alter the oligomerization state of NtrC or inhibit NtrC ATPase activity when bound to the PatzT promoter region. Taken together, these results strongly suggest that PatzT-bound AtzR interacts with NtrC to prevent the coupling of NtrC-mediated ATP hydrolysis with the remodeling of the interactions between E-σ(N) and PatzT that lead to open complex formation.
  
  
  
  Here, we describe a unique mechanism by which the regulatory protein AtzR prevents the activation of the σ(N)-dependent promoter PatzT Promoters of this family are always positively regulated, but there are a few examples of overlapping negative regulation. The mechanism described here is highly unconventional and involves an interaction between the repressor and activator proteins to prevent the action of the repressor protein on the RNA polymerase-promoter complex.
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, and Departamento de Biología Molecular e Ingeniería Bioquímica, Universidad Pablo de Olavide, Seville, Spain.
authors.forename: Ana Isabel
authors.initials: AI
authors.lastname: Platero
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, and Departamento de Biología Molecular e Ingeniería Bioquímica, Universidad Pablo de Olavide, Seville, Spain.
authors.forename: Aroa
authors.initials: A
authors.lastname: López-Sánchez
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, and Departamento de Biología Molecular e Ingeniería Bioquímica, Universidad Pablo de Olavide, Seville, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Tomás-Gallardo
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, and Departamento de Biología Molecular e Ingeniería Bioquímica, Universidad Pablo de Olavide, Seville, Spain.
authors.forename: Eduardo
authors.identifier: http://orcid.org/0000-0002-6111-7160
authors.initials: E
authors.lastname: Santero
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, and Departamento de Biología Molecular e Ingeniería Bioquímica, Universidad Pablo de Olavide, Seville, Spain fgovrom@upo.es.
authors.forename: Fernando
authors.initials: F
authors.lastname: Govantes
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D004269:DNA, Bacterial / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D009876:Operon; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011549:Pseudomonas / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D012808:Sigma Factor / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D004269:DNA, Bacterial; D012097:Repressor Proteins; D012808:Sigma Factor; D000255:Adenosine Triphosphate