Replisome bypass of transcription complexes and R-loops.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The genome is extensively transcribed by RNA polymerases.
• R-loops, formed by RNA invasion of DNA, can impede replication and destabilize the genome.
• The precise role of R-loops and associated factors in genome instability is not fully understood.

Purpose of the Study:

• To investigate the impact of replisome collisions with transcription complexes and R-loops on DNA replication.
• To determine if R-loops alone are sufficient to cause genome instability.

Main Methods:

• Utilized a reconstituted bacterial DNA replication system.
• Examined interactions between replication forks, RNA polymerase transcription complexes, and R-loops under various orientations.

Main Results:

• Co-directional transcription complexes caused transient replication blockages; head-on complexes caused severe, stable blockages.
• Replisomes readily bypassed R-loops on either DNA template strand.
• R-loops on the leading-strand template caused nascent strand gaps; lagging-strand template R-loops had minimal impact on fork progression.

Conclusions:

• R-loops alone act as transient replication blocks.
• Protein binding to R-loops is likely the primary driver of genome-destabilizing replication fork stalling.