G-quadruplex-stalled eukaryotic replisome structure reveals helical inchworm DNA translocation.

Area of Science:

• Molecular Biology
• Genetics
• Structural Biology

Background:

• DNA G-quadruplexes (G4s) are non-B DNA structures.
• G4s impede DNA replication, threatening genome stability.

Purpose of the Study:

• To elucidate the mechanism by which G4s cause replication fork arrest.
• To characterize G4-replisome interactions.

Main Methods:

• Reconstituted yeast and human replisomes were used to study fork collisions with G4s.
• Cryo-electron microscopy (Cryo-EM) determined the structures of stalled CMG complexes.

Main Results:

• A single G4 in the leading strand template arrests replisomes by stalling the CMG helicase.
• Cryo-EM structures show G4s lodged in the CMG central channel, blocking translocation.
• G4s stabilize CMG at specific intermediates, suggesting a helical inchworm translocation mechanism.

Conclusions:

• G4s arrest DNA replication by physically blocking the CMG helicase.
• This study reveals a novel mechanism for DNA translocation by CMG.
• Findings provide insight into eukaryotic replication fork dynamics under normal and perturbed conditions.