Undesigned selection for replication termination of bacterial chromosomes.

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Bacterial DNA replication involves a defined origin (oriC) but an often-obscure termination site.
• The terC locus is a known termination site in some bacteria, located opposite oriC and regulated by specific binding proteins.

Purpose of the Study:

• To investigate the robustness of the native terC function in Bacillus subtilis 168.
• To determine the factors influencing DNA replication termination site selection in bacteria.

Main Methods:

• Investigated Bacillus subtilis 168 strains with hindered replication axes.
• Examined strains with and without terminus region specific binding proteins.
• Validated findings using artificial chromosomes.

Main Results:

• Native terC function remained robust even when replication axes were hindered.
• Eliminating terminus region specific binding proteins led to termination at sites opposite oriC, not at natural terC sites.
• Replication termination consistently occurred at the meeting point of two equally-paced, approaching replisomes.

Conclusions:

• DNA replication termination is primarily determined by the meeting of two replisomes, a site automatically selected.
• Symmetrical chromosome structures relative to oriC are supported by equally-paced replisomes.
• This termination mechanism is likely general for replicons utilizing two replisomes, irrespective of oriC.