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FANCD2-FANCI surveys DNA and recognizes double- to single-stranded junctions

Pablo Alcón1, Artur P Kaczmarczyk2,3, Korak Kumar Ray2,3

  • 1MRC Laboratory of Molecular Biology, Cambridge, UK.

Nature
|July 31, 2024
PubMed

Insights

The FANCD2-FANCI (D2-I) complex acts as a sliding clamp, identifying DNA damage by stalling at single-stranded-double-stranded junctions at stalled replication forks to initiate repair.

Area of Science:

  • Molecular Biology
  • DNA Repair Mechanisms
  • Cellular Biology

Background:

  • DNA crosslinks impede DNA replication and are repaired via the Fanconi anemia pathway.
  • The FANCD2-FANCI (D2-I) complex is crucial for initiating DNA repair at crosslink lesions.
  • The D2-I complex also plays a general role in DNA repair and protects stalled replication forks from degradation.

Purpose of the Study:

  • To elucidate the mechanism of DNA crosslink recognition by the D2-I complex.
  • To understand how the D2-I complex functions in protecting stalled replication forks.
  • To reconcile the dual roles of D2-I in DNA repair and replication fork protection.

Main Methods:

  • Single-molecule imaging to observe D2-I dynamics on DNA.
  • Cryogenic electron microscopy (cryo-EM) to determine D2-I-DNA complex structures.
  • Analysis of D2-I interactions with double-stranded DNA and single-stranded-double-stranded junctions.

Main Results:

  • D2-I functions as a sliding clamp that diffuses along double-stranded DNA.
  • D2-I specifically stalls upon encountering single-stranded-double-stranded DNA junctions, characteristic of stalled replication forks.
  • Structural analysis revealed distinct D2-I interactions with ss-dsDNA junctions compared to dsDNA, enabling damage site recognition.

Conclusions:

  • D2-I identifies DNA damage sites by recognizing and clamping onto ss-dsDNA junctions at stalled replication forks.
  • This mechanism provides a unified understanding of D2-I's roles in DNA repair and replication fork protection.
  • The findings offer insights into Fanconi anemia pathway and broader DNA damage response mechanisms.

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