RADX condenses single-stranded DNA to antagonize RAD51 loading

Nucleic Acids Res. 2020 Aug 20;48(14):7834-7843. doi: 10.1093/nar/gkaa559.


RADX is a mammalian single-stranded DNA-binding protein that stabilizes telomeres and stalled replication forks. Cellular biology studies have shown that the balance between RADX and Replication Protein A (RPA) is critical for DNA replication integrity. RADX is also a negative regulator of RAD51-mediated homologous recombination at stalled forks. However, the mechanism of RADX acting on DNA and its interactions with RPA and RAD51 are enigmatic. Using single-molecule imaging of the key proteins in vitro, we reveal that RADX condenses ssDNA filaments, even when the ssDNA is coated with RPA at physiological protein ratios. RADX compacts RPA-coated ssDNA filaments via higher-order assemblies that can capture ssDNA in trans. Furthermore, RADX blocks RPA displacement by RAD51 and prevents RAD51 loading on ssDNA. Our results indicate that RADX is an ssDNA condensation protein that inhibits RAD51 filament formation and may antagonize other ssDNA-binding proteins on RPA-coated ssDNA.

Publication types

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

MeSH terms

  • DNA, Single-Stranded / metabolism*
  • DNA-Binding Proteins / metabolism*
  • Humans
  • Rad51 Recombinase / metabolism*
  • Replication Protein A / metabolism
  • Single Molecule Imaging


  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • Replication Protein A
  • RAD51 protein, human
  • Rad51 Recombinase