# An essential gene screening identifies yeast Mot1 as a suppressor of R-loops and genome instability

## TL;DR

This study identifies the yeast protein Mot1 as a key suppressor of R-loops and genome instability, particularly during DNA replication.

## Contribution

The study reveals a novel role for the essential protein Mot1 in preventing R-loop accumulation and genome instability during S phase.

## Key findings

- Mot1 prevents R-loop accumulation and genome instability, especially during DNA replication.
- Mot1 dysfunction leads to replication impairment likely due to transcription-replication conflicts.
- Genetic evidence supports Mot1's role in resolving transcription-replication conflicts via R-loop regulation.

## Abstract

Transcription is essential for cellular function, but it can also lead to genetic instability, particularly through the formation of secondary structures such as R-loops, which consist of an RNA-DNA hybrid and a displaced DNA strand. Unscheduled R-loop accumulation is a major source of DNA damage and has been associated with several human diseases, including cancer. While multiple factors involved in RNA biogenesis, export, and chromatin remodeling play a role in preventing R-loop accumulation, the function of essential proteins in R-loop metabolism remains unexplored. Here, we performed a genetic screening in Saccharomyces cerevisiae using over 1200 temperature-sensitive mutants to identify novel proteins involved in the prevention of R-loop-associated genomic instability. Our results reveal that the SWI/SNF-like protein Mot1 plays a key role in preventing R-loop accumulation and R-loop-associated genome instability. Its role is particularly important during S phase, where Mot1 dysfunction leads to R-loop dependent replication impairment, presumably due to transcription-replication conflicts (TRCs). Epistatic relationships between mutations in MOT1 and the S-phase specific DNA-RNA helicase SEN1 further support the role of Mot1 in TRCs. The study highlights the importance of transcriptional regulators in maintaining genome stability by mitigating TRCs and regulating R-loop homeostasis.

The maintenance of genome integrity is crucial to safeguard organism viability and avoid diseases. During the process of transcription, secondary structures known as R-loops, which consist of an RNA-DNA hybrid and a displaced DNA strand, may be formed. Such structures have been shown to interfere with other DNA-templated processes, including replication, thus resulting in genetic instability. Multiple factors implicated in the processes of RNA biogenesis, export, and chromatin remodeling have been shown to exert a function in the prevention of R-loop accumulation; however, the role of essential proteins in R-loop metabolism remained unexplored. In this study, budding yeast was used as eukaryotic model organism to perform a genetic screening with the aim of identifying essential proteins involved in the prevention of R-loop-associated genomic instability. We found that the Mot1 transcription factor plays a key role in preventing R-loop accumulation and R-loop-associated genome instability. Our results showed that its role is particularly important during S phase, where Mot1 dysfunction affects replication fork progression. We provide genetic and molecular evidence that these defects are primarily attributable to transcription-replication conflicts mediated by R-loops. Our study highlights the significance of transcriptional regulators in preserving genome stability by mitigating transcription-replication conflicts and regulating R-loop homeostasis.