Distinct replication requirements for the two Vibrio cholerae chromosomes

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Prokaryotic chromosome replication studies have predominantly focused on single-chromosome organisms.
• Understanding replication in multi-chromosome bacteria like Vibrio cholerae presents unique challenges.

Purpose of the Study:

• To define and characterize the origins of replication (oriCI(vc) and oriCII(vc)) for the two chromosomes of Vibrio cholerae.
• To elucidate the mechanisms controlling replication initiation and regulation in this bacterium.

Main Methods:

• Comparative genomics and bioinformatic analysis to predict origins.
• Experimental characterization of replication origins and flanking regions.
• Investigation of gene functions and regulatory elements involved in replication.

Main Results:

• Identified and characterized two distinct origins of replication: oriCI(vc) and oriCII(vc).
• OriCII(vc) differs from bioinformatic predictions and is unrelated to oriCI(vc).
• OriCII(vc) replication involves a 12 base pair repeat, flanking genes (one encoding an origin binding protein, the other an RNA), and negative regulation by an adjacent DNA sequence.
• Both oriCI(vc) and oriCII(vc) replication require DNA adenine methyltransferase, a novel finding.

Conclusions:

• Vibrio cholerae utilizes distinct replication origins and regulatory mechanisms for its two chromosomes.
• The findings suggest that multi-chromosome microorganisms may employ unique strategies for replication control.
• DNA adenine methyltransferase plays a critical, previously unrecognized role in the replication of both Vibrio cholerae chromosomes.