The SNM1B/APOLLO DNA nuclease functions in resolution of replication stress and maintenance of common fragile site stability

Hum Mol Genet. 2013 Dec 15;22(24):4901-13. doi: 10.1093/hmg/ddt340. Epub 2013 Jul 17.


SNM1B/Apollo is a DNA nuclease that has important functions in telomere maintenance and repair of DNA interstrand crosslinks (ICLs) within the Fanconi anemia (FA) pathway. SNM1B is required for efficient localization of key repair proteins, such as the FA protein, FANCD2, to sites of ICL damage and functions epistatically to FANCD2 in cellular survival to ICLs and homology-directed repair. The FA pathway is also activated in response to replication fork stalling. Here, we sought to determine the importance of SNM1B in cellular responses to stalled forks in the absence of a blocking lesion, such as ICLs. We found that depletion of SNM1B results in hypersensitivity to aphidicolin, a DNA polymerase inhibitor that causes replication stress. We observed that the SNM1B nuclease is required for efficient localization of the DNA repair proteins, FANCD2 and BRCA1, to subnuclear foci upon aphidicolin treatment, thereby indicating SNM1B facilitates direct repair of stalled forks. Consistent with a role for SNM1B subsequent to recognition of the lesion, we found that SNM1B is dispensable for upstream events, including activation of ATR-dependent signaling and localization of RPA, γH2AX and the MRE11/RAD50/NBS1 complex to aphidicolin-induced foci. We determined that a major consequence of SNM1B depletion is a marked increase in spontaneous and aphidicolin-induced chromosomal gaps and breaks, including breakage at common fragile sites. Thus, this study provides evidence that SNM1B functions in resolving replication stress and preventing accumulation of genomic damage.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Aphidicolin / pharmacology
  • BRCA1 Protein / metabolism
  • Cell Line
  • Cell Nucleus / metabolism
  • Cell Survival / drug effects
  • Cell Survival / genetics
  • Chromatin / metabolism
  • Chromosome Fragile Sites*
  • DNA Damage
  • DNA Repair
  • DNA Repair Enzymes / chemistry
  • DNA Repair Enzymes / genetics
  • DNA Repair Enzymes / metabolism*
  • DNA Replication*
  • Exodeoxyribonucleases
  • Fanconi Anemia Complementation Group D2 Protein / metabolism
  • Gene Expression
  • Genomic Instability*
  • Histones / metabolism
  • Humans
  • Multiprotein Complexes / metabolism
  • Nuclear Proteins / chemistry
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Transport
  • Replication Protein A / metabolism
  • Signal Transduction / drug effects
  • Ubiquitination


  • BRCA1 Protein
  • Chromatin
  • Fanconi Anemia Complementation Group D2 Protein
  • H2AX protein, human
  • Histones
  • Multiprotein Complexes
  • Nuclear Proteins
  • Replication Protein A
  • Aphidicolin
  • DCLRE1B protein, human
  • Exodeoxyribonucleases
  • DNA Repair Enzymes