Two components of DNA replication-dependent LexA cleavage

Area of Science:

• Bacteriology
• Molecular Biology
• Genetics

Background:

• The SOS response in bacteria is a crucial DNA damage repair mechanism.
• This response is initiated by the formation of single-stranded DNA (ssDNA) during replication.
• RecA protein binding to ssDNA is essential for activating downstream repair pathways by cleaving the LexA repressor.

Purpose of the Study:

• To investigate the mechanisms of LexA cleavage during DNA replication of both undamaged and damaged DNA templates.
• To identify the specific DNA structures and proteins involved in SOS induction during replication.

Main Methods:

• Utilized an in vitro reconstituted DNA replication system.
• Performed LexA cleavage assays using both undamaged and base-damaged DNA templates.
• Analyzed the role of RecA, ssDNA, and RecF in LexA cleavage during replication.

Main Results:

• LexA cleavage was dependent on the formation of ssDNA-RecA filaments.
• Replication of undamaged DNA induced LexA cleavage comparable to damaged templates.
• Two pathways generating ssDNA were identified: polymerase-helicase uncoupling and replisome lesion skipping, with RecF specifically aiding the latter.

Conclusions:

• ssDNA generation during normal replication and due to replication stress both contribute to SOS induction.
• RecF protein plays a specific role in facilitating RecA filament formation on ssDNA gaps arising from replisome lesion skipping on damaged DNA.