Sae2/CtIP prevents R-loop accumulation in eukaryotic cells

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Sae2/CtIP protein is crucial for DNA double-strand break repair via homologous recombination.
• It also plays a role in surviving single-stranded DNA lesions induced by Top1.
• CtIP associates with transcription complexes in mammalian cells.

Purpose of the Study:

• Investigate the function of Sae2/CtIP at single-strand DNA lesions in yeast and human cells.
• Determine the role of Sae2/CtIP in R-loop formation and processing.
• Elucidate the mechanism by which Sae2/CtIP contributes to genome stability.

Main Methods:

• Depletion of Sae2/CtIP in budding yeast and human cells.
• Analysis of stalled RNA polymerase and RNA-DNA hybrid accumulation.
• Overexpression of Senataxin (RNA-DNA helicase) to assess its effect.
• Complementation studies using a catalytic mutant of CtIP.

Main Results:

• Depletion of Sae2/CtIP leads to accumulation of stalled RNA polymerase and RNA-DNA hybrids at highly expressed genes.
• Overexpression of Senataxin rescues DNA damage sensitivity and R-loop accumulation in Sae2/CtIP-deficient cells.
• A catalytically inactive CtIP mutant cannot restore DNA damage resistance, indicating a requirement for CtIP nuclease activity.

Conclusions:

• Sae2/CtIP plays a critical role in processing single-strand DNA lesions and preventing R-loop accumulation.
• R-loop processing by 5' flap endonucleases is essential for stabilizing and removing nascent R-loop structures.
• This highlights a conserved mechanism for maintaining genome integrity during transcription and DNA repair.