Interplay Between DNA Polymerase, RNA Polymerase, and RNase H1 During Head-On Transcription-Replication Conflict

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Transcription-replication conflicts (TRCs) are common cellular events that can lead to DNA replication fork stalling.
• Understanding the molecular mechanisms governing TRCs is crucial for comprehending genome stability.

Purpose of the Study:

• To investigate the in vitro interplay between RNA polymerase (RNAP), DNA polymerase (including Klenow fragment and DNA Pol I), and RNase H1 (RH1) during head-on TRCs.
• To elucidate how different states of RNAP complexes and R-loops affect DNA replication and transcription dynamics.

Main Methods:

• In vitro biochemical assays were employed to precisely control reaction conditions.
• The study utilized Klenow fragment, full-length DNA Pol I, and RNase H1 to analyze their interactions with transcription elongation complexes (TECs) and R-loops.

Main Results:

• A catalytically competent TEC interferes with DNA polymerase action, while an incompetent RNAP complex with an R-loop stimulates DNA polymerase exonuclease activity and causes pausing.
• Isolated R-loops (R-loop-11) did not stall Klenow fragment but stimulated DNA Pol I exonuclease activity.
• Stalled Klenow fragment did not affect transcription, but moving Klenow altered RNAP kinetics. Stalled DNA Pol I stimulated RNAP endonuclease activity.
• RNase H1 alone did not resolve competent TEC-associated TRCs but displaced RNAP from incompetent complexes, thereby reducing DNA polymerase exonuclease activity stimulation.

Conclusions:

• The catalytic state of RNAP and the presence of R-loops critically modulate the outcome of head-on TRCs.
• RNase H1's efficacy in resolving TRCs is dependent on the specific complex formed between RNAP and the DNA/RNA hybrid.
• These findings provide insights into the dynamic molecular interactions that govern genome stability during conflicts between transcription and replication.