IHF-binding sites inhibit DNA loop formation and transcription initiation

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Enhancer-dependent transcription requires DNA looping between enhancer-binding proteins and sigma(54)-RNA polymerase.
• Integration host factor (IHF) typically facilitates this DNA looping.
• The specific role of IHF in regulating transcription initiation frequency remains unclear.

Purpose of the Study:

• To investigate the precise role of IHF in DNA looping and transcriptional activation.
• To determine how IHF influences the efficiency of DNA-loop formation at sigma(54)-dependent promoters.

Main Methods:

• Kinetic cyclization assays to measure DNA looping ability.
• In vitro transcription assays to assess transcriptional activation.
• Site-directed mutagenesis to introduce or remove IHF-binding sites.

Main Results:

• DNA fragments with IHF-binding sites showed reduced looping ability in the absence of IHF.
• Introducing an IHF consensus-binding site into the intervening DNA region decreased loop formation and looping-dependent transcription.
• IHF binding restored efficient DNA looping and transcriptional activation.

Conclusions:

• IHF acts to overcome a communication block imposed by its own DNA-binding site.
• This function of IHF is crucial for efficient DNA looping and transcriptional activation of sigma(54)-dependent promoters.
• IHF's role extends beyond simply facilitating looping to actively resolving inhibitory DNA-intrinsic properties.