Processing of Reversed Replication Forks is Required for the Resolution of Replication-Transcription Conflicts

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA replication and transcription can conflict, stalling replication forks and causing genome instability.
• Head-on conflicts between replication and transcription are more detrimental than co-directional ones.
• The impact of these conflicts on replication fork structure is not fully understood.

Purpose of the Study:

• To identify essential factors for surviving head-on replication-transcription conflicts in *Bacillus subtilis*.
• To elucidate the role of the AddAB complex in resolving these conflicts.

Main Methods:

• Unbiased genetic screen using a transposon library in *Bacillus subtilis*.
• Follow-up genetic and biochemical analyses of identified factors.
• Investigated the role of RNase HIII, AddA, and AddB.

Main Results:

• The screen identified RNase HIII, AddA, and AddB as essential for surviving head-on conflicts.
• AddA and AddB, functioning as the AddAB complex, were identified as essential conflict resolution factors.
• Helicase activity of AddAB, not nuclease activity, is crucial for resolving head-on conflicts.

Conclusions:

• AddAB unwinds nascent strands forming a reversed fork structure during head-on conflicts.
• This unwinding facilitates re-annealing to parental strands, restarting replication.
• AddAB is a key factor in resolving head-on replication-transcription conflicts, maintaining genome stability.