Cohesin SA2 is a sequence-independent DNA-binding protein that recognizes DNA replication and repair intermediates

Preston Countryman, Yanlin Fan, Aparna Gorthi, Hai Pan, Jack Strickland, Parminder Kaur, Xuechun Wang, Jiangguo Lin, Xiaoying Lei, Christian White, Changjiang You, Nicolas Wirth, Ingrid Tessmer, Jacob Piehler, Robert Riehn, Alexander J.R. Bishop, Yizhi Jane Tao, Hong Wang

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Proper chromosome alignment and segregation during mitosis depend on cohesion between sister chromatids, mediated by the cohesin protein complex, which also plays crucial roles in diverse genome maintenance pathways. Current models attribute DNA binding by cohesin to entrapment of dsDNA by the cohesin ring subunits (SMC1, SMC3, and RAD21 in humans). However, the biophysical properties and activities of the fourth core cohesin subunit SA2 (STAG2) are largely unknown. Here, using single-molecule atomic force and fluorescence microscopy imaging as well as fluorescence anisotropy measurements, we established that SA2 binds to both dsDNA and ssDNA, albeit with a higher binding affinity for ssDNA. We observed that SA2 can switch between the 1D diffusing (search) mode on dsDNA and stable binding (recognition) mode at ssDNA gaps. Although SA2 does not specifically bind to centromeric or telomeric sequences, it does recognize DNA structures often associated with DNA replication and double-strand break repair, such as a double-stranded end, single-stranded overhang, flap, fork, and ssDNA gap. SA2 loss leads to a defect in homologous recombination–mediated DNA double-strand break repair. These results suggest that SA2 functions at intermediate DNA structures during DNA transactions in genome maintenance pathways. These findings have important implications for understanding the function of cohesin in these pathways.

Original languageEnglish (US)
Pages (from-to)1054-1069
Number of pages16
JournalJournal of Biological Chemistry
Issue number3
StatePublished - Jan 19 2018

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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