The Caulobacter crescentus chromosome replication origin evolved two classes of weak DnaA binding sites

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Chromosome replication initiation is tightly regulated in bacteria.
• The proteins DnaA and CtrA play critical roles in controlling DNA replication in Caulobacter crescentus.
• The replication origin (Cori) in C. crescentus has an unusual distribution of binding sites for these regulatory proteins.

Purpose of the Study:

• To investigate the DNA binding sites and mechanisms of the replication initiator DnaA in Caulobacter crescentus.
• To understand how DnaA and CtrA compete and cooperate to regulate chromosome replication.
• To identify novel DNA sequences recognized by DnaA at the replication origin.

Main Methods:

• Scanning mutagenesis of conserved Cori DNA sequences.
• Autonomous replication assays to test the function of identified DNA sites.
• In vitro binding assays to determine the affinities of DnaA for different DNA sequences.
• Cell cycle analysis to correlate protein activity with DNA replication.

Main Results:

• Identified novel W-boxes (TCCCCA) as essential replication sites alongside known DnaA boxes (G-boxes).
• Demonstrated that Caulobacter crescentus DnaA binds G-boxes with moderate affinity and W-boxes with very weak affinity.
• Showed that CtrA binding can displace DnaA from Cori, indicating competition.
• Observed that strategically positioned weak DnaA binding sites are conserved in other bacterial replication origins.

Conclusions:

• Bacterial replication origins can utilize strategically weak DnaA binding sites for precise control.
• The interplay between DnaA and CtrA at Cori is essential for regulating DNA replication initiation.
• Weak DnaA binding represents a general mechanism for controlling DNA replication across different bacterial species.