DNA and Chromosomes
Structural mechanism of DNA interstrand cross-link unhooking by the bacterial FAN1 nuclease
DNA interstrand cross-links (ICLs) block the progress of the replication and transcription machineries and can weaken chromosomal stability, resulting in various diseases. FANCD2–FANCI-associated nuclease (FAN1) is a conserved structure-specific nuclease that unhooks DNA ICLs independently of the Fanconi anemia pathway. Recent structural studies have proposed two different mechanistic features for ICL unhooking by human FAN1: a specific basic pocket that recognizes the terminal phosphate of a 1-nucleotide (nt) 5′ flap or FAN1 dimerization.Bypass of DNA-Protein Cross-links Conjugated to the 7-Deazaguanine Position of DNA by Translesion Synthesis Polymerases
DNA-protein cross-links (DPCs) are bulky DNA lesions that form both endogenously and following exposure to bis-electrophiles such as common antitumor agents. The structural and biological consequences of DPCs have not been fully elucidated due to the complexity of these adducts. The most common site of DPC formation in DNA following treatment with bis-electrophiles such as nitrogen mustards and cisplatin is the N7 position of guanine, but the resulting conjugates are hydrolytically labile and thus are not suitable for structural and biological studies.FANCD2-associated Nuclease 1, but Not Exonuclease 1 or Flap Endonuclease 1, Is Able to Unhook DNA Interstrand Cross-links in Vitro
Background: We studied how the endo/exonucleases EXO1, FAN1, and FEN1 process substrates resembling replication forks blocked by interstrand cross-links (ICLs).Results: All three enzymes cleaved off the single-stranded 5′ flap, but FAN1 was also able to incise the substrate behind the ICL.Conclusion: FAN1 can unhook ICLs.Significance: In vivo, FAN1 may not require a 3′ flap nuclease to unhook ICLs.
