Multistep mechanism of G-quadruplex resolution during DNA replication

Area of Science:

• Genetics
• Molecular Biology
• Genomics

Background:

• G-quadruplex (G4) structures arise from guanine-rich DNA sequences.
• Unresolved G4s pose a threat to genome stability.
• G4 unwinding during S phase replication is essential but poorly understood.

Purpose of the Study:

• To elucidate the mechanism of G4 unwinding during DNA replication.
• To identify the molecular players involved in G4 resolution.
• To understand how genome stability is maintained in the presence of G4 structures.

Main Methods:

• Utilized Xenopus egg extracts to model DNA replication.
• Investigated the roles of replicative helicases (CMG), DHX36, and FANCJ in G4 processing.
• Analyzed G4 structures on both leading and lagging strands during replication.

Main Results:

• Defined a three-step G4 unwinding mechanism during replication.
• CMG helicase stalls at leading strand G4s, bypassed by DHX36.
• FANCJ unwinds G4s, enabling DNA polymerase to proceed; DHX36 and FANCJ show partial redundancy.
• Lagging strand G4s do not stall CMG but require replication for unwinding.

Conclusions:

• Identified a novel genome maintenance pathway for faithful G4 replication.
• This pathway prevents genome instability by ensuring proper G4 resolution.
• DHX36 and FANCJ contribute to pathway robustness through partially redundant functions.