RECQ-like helicases Sgs1 and BLM regulate R-loop-associated genome instability

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Sgs1 is a yeast DNA helicase, homologous to human Bloom's syndrome helicase (BLM), crucial for DNA replication and repair.
• R-loops, DNA:RNA hybrids, can form during transcription and pose a threat to genome stability.

Purpose of the Study:

• To investigate the role of Sgs1/BLM in suppressing R-loop accumulation and associated genome instability.
• To determine if Sgs1/BLM's function in R-loop suppression is conserved across species.

Main Methods:

• Yeast genetics to study SGS1 loss-of-function mutants.
• Analysis of R-loop and γ-H2A accumulation in yeast cells.
• Mutation signature analysis of sgs1Δ.
• Studies in Bloom's syndrome fibroblasts and BLM-depleted human cancer cells.
• In vitro R-loop unwinding assays with BLM.

Main Results:

• SGS1 loss in yeast leads to increased R-loop accumulation and sensitivity to transcription-replication collisions.
• R-loops and γ-H2A accumulate at specific genomic regions in sgs1Δ cells, including replication pausing sites and long genes.
• Mutation signatures in sgs1Δ cells indicate copy number changes near repetitive, R-loop-prone regions.
• BLM plays a conserved role in suppressing R-loop-associated genome instability in human cells.
• BLM is found near DNA:RNA hybrids and can unwind R-loops in vitro.

Conclusions:

• Sgs1/BLM is a conserved suppressor of R-loop accumulation and genome instability.
• DNA repair and replication fork stabilizing proteins, like Sgs1/BLM, modulate R-loop-mediated genomic instability.
• These findings broaden the understanding of DNA repair proteins' roles in maintaining genome integrity.