SbcC-SbcD and ExoI process convergent forks to complete chromosome replication

Area of Science:

• * Molecular Biology
• * Genetics
• * Biochemistry

Background:

• * SbcC-SbcD is the bacterial ortholog of the Mre11-Rad50 nuclease complex, crucial for mammalian genome stability.
• * In vitro studies show SbcC-SbcD and ExoI degrade long DNA palindromes, but their in vivo substrates and functions remain unclear.
• * Palindromic amplifications occur in bacteria and eukaryotes when these nucleases are inactivated.

Purpose of the Study:

• * To elucidate the in vivo function of SbcC-SbcD and ExoI in bacterial genome maintenance.
• * To identify the cellular substrates and critical cellular processes involving these nucleases.
• * To understand the consequences of impaired nucleolytic processing during DNA replication.

Main Methods:

• * Investigated the role of SbcC-SbcD and ExoI during DNA replication completion in *Escherichia coli*.
• * Analyzed the formation of structural intermediates at convergent replication forks.
• * Examined cellular responses, including aberrant recombination and genomic instability, upon nuclease inactivation.

Main Results:

• * Convergent replication forks create a palindrome-like intermediate requiring SbcC-SbcD and ExoI processing for replication completion.
• * Inactivation of SbcC-SbcD and ExoI prevents replication completion, leading to cell viability through an aberrant recombinational pathway.
• * This pathway results in DNA amplifications and genomic instability in the affected chromosomal region.
• * SbcC-SbcD-ExoI acts upstream of RecBCD, initiating the replication completion process.

Conclusions:

• * Replication completion is a critical process for maintaining genome integrity and cell viability.
• * SbcC-SbcD and ExoI are essential nucleases that process replication intermediates to ensure proper chromosome replication.
• * Defects in replication completion lead to genomic instability and amplifications via aberrant recombination pathways.