Mammalian CST averts replication failure by preventing G-quadruplex accumulation.

Area of Science:

• Molecular Biology
• Genetics
• DNA Replication

Background:

• The human CST (CTC1-STN1-TEN1) complex interacts with G-rich single-strand DNA.
• CST is known to help resolve replication problems at telomeres and genome-wide.
• Previous in vitro studies showed CST disrupts G-quadruplex (G4) DNA structures.

Purpose of the Study:

• To investigate the in vivo role of CST in resolving G-quadruplex (G4) DNA structures.
• To determine CST's function in preventing replication blocks caused by G4s.
• To elucidate CST's contribution to maintaining genome and telomere integrity.

Main Methods:

• Assessed CST's G4 binding and unfolding efficiency compared to RPA.
• Observed CST recruitment to chromatin upon G4 stabilization in cells, even with ATR/ATM inhibition.
• Utilized STN1 depletion and G4 stabilization to study telomere replication, employing multi-telomere FISH and BrdU incorporation assays.

Main Results:

• CST binds and unfolds G4 DNA with efficiency comparable to RPA.
• CST is recruited to telomeric and non-telomeric chromatin when G4s are stabilized.
• STN1 depletion leads to increased G4 accumulation, slowed DNA replication, and telomere loss, specifically affecting C-strand and lagging strand synthesis.

Conclusions:

• CST plays a crucial role in resolving G4 structures, preventing replication fork stalling.
• CST is essential for maintaining telomere duplex replication and overall genome integrity.
• Findings reveal a novel function for CST in resolving G4s ahead of the fork and on the lagging strand template.