Slx1-Slx4 is a second structure-specific endonuclease functionally redundant with Sgs1-Top3

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• RecQ DNA helicases, like human BLM and yeast Sgs1, partner with DNA topoisomerase III.
• These complexes are vital for resolving stalled replication forks and preserving genome stability.
• SLX1 and SLX4 are essential for rDNA replication when SGS1-TOP3 is absent.

Purpose of the Study:

• To elucidate the mechanism by which SLX1 and SLX4 function in DNA replication and stability.
• To characterize the enzymatic activity and subunit interactions of the Slx1-Slx4 complex.
• To understand the role of Slx1-Slx4 in DNA repair pathways.

Main Methods:

• Biochemical assays to determine nuclease activity on various DNA substrates.
• In vitro and in vivo experiments to assess the roles of Slx1, Slx4, and the PHD finger.
• Analysis of cell viability and DNA damage resistance in response to methylmethane sulfonate (MMS).

Main Results:

• SLX1 and SLX4 form a heteromeric structure-specific endonuclease, the Slx1-Slx4 nuclease.
• The Slx1-Slx4 nuclease efficiently cleaves branched DNA structures, including Y-shaped, 5'-flap, and replication fork substrates.
• Slx4 significantly stimulates Slx1's endonuclease activity, with the PHD finger being essential for both in vitro and in vivo function.
• Both Slx1 and Slx4 are indispensable for cellular resistance to methylmethane sulfonate (MMS)-induced DNA damage.

Conclusions:

• The Slx1-Slx4 complex acts as a structure-specific endonuclease on stalled replication forks.
• In the absence of Sgs1-Top3, Slx1-Slx4 is proposed to cleave stalled forks, preventing genome instability.
• This pathway highlights a critical DNA repair mechanism involving specialized nucleases for maintaining genomic integrity.