The SOSS1 single-stranded DNA binding complex promotes DNA end resection in concert with Exo1

EMBO J. 2013 Jan 9;32(1):126-39. doi: 10.1038/emboj.2012.314. Epub 2012 Nov 23.


The human SSB homologue 1 (hSSB1) has been shown to facilitate homologous recombination and double-strand break signalling in human cells. Here, we compare the DNA-binding properties of the SOSS1 complex, containing SSB1, with Replication Protein A (RPA), the primary single-strand DNA (ssDNA) binding complex in eukaryotes. Ensemble and single-molecule approaches show that SOSS1 binds ssDNA with lower affinity compared to RPA, and exhibits less stable interactions with DNA substrates. Nevertheless, the SOSS1 complex is uniquely capable of promoting interaction of human Exo1 with double-strand DNA ends and stimulates its activity independently of the MRN complex in vitro. Both MRN and SOSS1 also act to mitigate the inhibitory action of the Ku70/80 heterodimer on Exo1 activity in vitro. These results may explain why SOSS complexes do not localize with RPA to replication sites in human cells, yet have a strong effect on double-strand break resection and homologous recombination.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Antigens, Nuclear / genetics
  • Antigens, Nuclear / metabolism
  • DNA / metabolism*
  • DNA Breaks, Double-Stranded
  • DNA Repair
  • DNA Repair Enzymes / genetics
  • DNA Repair Enzymes / metabolism*
  • DNA Replication
  • DNA, Single-Stranded / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Eukaryotic Cells
  • Exodeoxyribonucleases / genetics
  • Exodeoxyribonucleases / metabolism*
  • Fluorescence Resonance Energy Transfer
  • Homologous Recombination
  • Humans
  • Ku Autoantigen
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism*
  • Multiprotein Complexes
  • Protein Binding
  • Protein Multimerization
  • Replication Protein A / genetics
  • Replication Protein A / metabolism*
  • Signal Transduction


  • Antigens, Nuclear
  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • Mitochondrial Proteins
  • Multiprotein Complexes
  • RPA1 protein, human
  • Replication Protein A
  • SSBP1 protein, human
  • DNA
  • EXO1 protein, human
  • Exodeoxyribonucleases
  • Xrcc6 protein, human
  • Ku Autoantigen
  • DNA Repair Enzymes