Harmful R-loops are prevented via different cell cycle-specific mechanisms

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• R-loops, or DNA:RNA hybrids, are implicated in compromising genome integrity during transcription.
• Understanding the mechanisms of R-loop formation and resolution is critical for comprehending DNA damage during replication.

Purpose of the Study:

• To elucidate the roles of the THO transcription complex and Sen1 DNA-RNA helicase in preventing and resolving R-loop formation.
• To determine the cell-cycle dependency of R-loop regulation by THO and Sen1.

Main Methods:

• Genome-wide analysis of conditional yeast mutants.
• Assessing R-loop formation and DNA damage accumulation in relation to the cell cycle.

Main Results:

• The THO complex prevents R-loop formation in both G1 and S-phases, acting as a general safeguard.
• Sen1, a DNA-RNA helicase, resolves R-loops specifically during S-phase.
• DNA damage accumulates asymmetrically downstream of the replication fork in sen1 mutants, but symmetrically in THO (hpr1) mutants.

Conclusions:

• R-loops form co-transcriptionally, independent of DNA replication.
• THO functions as a cell-cycle-independent factor against R-loops.
• Sen1 acts as an S-phase-specific R-loop resolvase, challenging previous assumptions.
• These findings impact our understanding of R-loop homeostasis and genome stability mechanisms.