Two roles for integration host factor at an enhancer-dependent nifA promoter.
Control of transcription in prokaryotes often involves direct contact of regulatory proteins with RNA polymerase. For the sigma54 RNA polymerase, regulatory proteins bound to distally located enhancers engage the polymerase via DNA looping. The sigma54-dependent nifA promoter of Herbaspirillum seropedicae (Hs) is activated under nitrogen-limiting growth conditions. Potential enhancers for the nitrogen control activators NTRC and NIFA and binding sites for integration host factor (IHF) and sigma54-holoenzyme were identified. DNA footprinting experiments showed that these sites functioned for protein binding. Their involvement in the promoter regulation was explored. In vitro, activation of the Hs nifA promoter by NTRC is stimulated by the DNA bending protein IHF. In marked contrast, activation by NIFA is greatly reduced by IHF, thus diminishing potentially destabilizing autoactivation of the nifA promoter by NIFA. Additionally, high levels of NIFA appear to limit NTRC-dependent activation. This inhibition is IHF dependent. Therefore, IHF acts positively and negatively at the nifA promoter to restrict transcription activation to NTRC and one signal transduction pathway.
Wassem
R
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Departamento de Bioquímica, Universidade Federal do Paraná, Caixa Postal 19046, Curitiba - PR, CEP 81531-990, Brazil.
De Souza
E M
EM
Yates
M G
MG
Pedrosa
F D
FD
Buck
M
M
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000494:pharmacology; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D006090:Gram-Negative Bacteria / Q000235:genetics / Q000378:metabolism; D034982:Integration Host Factors; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009711:Nucleotides / Q000494:pharmacology; D051922:PII Nitrogen Regulatory Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D051877:RNA Polymerase Sigma 54; D012808:Sigma Factor / Q000378:metabolism; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D034982:Integration Host Factors; C061338:NifA protein, Bacteria; D009711:Nucleotides; D051922:PII Nitrogen Regulatory Proteins; D012808:Sigma Factor; D015534:Trans-Activators; D014157:Transcription Factors; D004247:DNA; D012321:DNA-Directed RNA Polymerases; D051877:RNA Polymerase Sigma 54