A dual binding site for integration host factor and the response regulator CtrA inside the Caulobacter crescentus...

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The response regulator CtrA is crucial for controlling chromosome replication initiation in Caulobacter crescentus.
• CtrA binds to multiple sites within the replication origin (Cori), including sites a, b, c, d, and e.

Purpose of the Study:

• To investigate the role of integration host factor (IHF) in regulating CtrA binding at the Cori.
• To understand the functional consequences of IHF-CtrA interactions at the replication origin.

Main Methods:

• DNA-protein binding assays to analyze IHF and CtrA interactions at Cori.
• Site-directed mutagenesis of the CtrA/IHF binding site within Cori.
• Assessing the impact of mutations on plasmid replication and chromosomal growth.
• Analyzing transcriptional changes in response to mutations in the CtrA/IHF site.

Main Results:

• IHF binds to Cori at the central CtrA binding site c, sharing DNA recognition sequences with CtrA.
• IHF binding inhibits CtrA binding to sites c and d, rather than promoting cooperative binding.
• Mutations in the CtrA c/IHF site impair autonomous Cori plasmid replication and alter distant promoter transcription.
• Deletion of the CtrA c/IHF site from the chromosome leads to slow growth and intolerance to a CtrA phosphor-mimic allele.

Conclusions:

• IHF plays a regulatory role by competing with CtrA at the Cori.
• The interplay between IHF and CtrA is essential for efficient chromosome replication, potentially involving DNA bending.
• Cell cycle-dependent expression of IHF and CtrA suggests a dynamic mechanism for replication control.