RecBCD, SbcCD and ExoI process a substrate created by convergent replisomes to complete DNA replication

Area of Science:

• Molecular Biology
• Genetics
• DNA Replication

Background:

• Accurate DNA replication is crucial for genomic stability.
• The roles of RecBCD, SbcCD, and ExoI nucleases in replication completion are not fully understood.
• Previous studies have not identified the specific substrates or mechanisms involved in replication completion.

Purpose of the Study:

• To investigate the substrates and mechanisms of DNA replication completion enzymes.
• To determine the necessity of RecBCD, SbcCD, and ExoI in resolving replication fork convergence.
• To elucidate the relationship between replication completion and genomic instability.

Main Methods:

• Utilized plasmid substrates with one or two converging replisomes.
• Assessed the requirement for RecBCD, RecA, SbcCD, and ExoI in replication completion.
• Analyzed DNA intermediates and genomic instability, including amplifications.

Main Results:

• Replication completion enzymes function on substrates with two converging replisomes but not one.
• RecBCD is essential for completion, while RecA is not required, and no double-strand breaks accumulate.
• Inhibition of normal completion triggers aberrant RecA-mediated recombination, leading to amplifications and instability.

Conclusions:

• The substrate for SbcCD, ExoI, and RecBCD is specifically generated by two convergent replication forks.
• RecBCD's role in replication completion is independent of double-strand break repair.
• Replication completion likely involves the joining of strands from convergent replication forks, preventing instability.