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

Autor(en): Countryman, Preston
Fan, Yanlin
Gorthi, Aparna
Pan, Hai
Strickland, Jack
Kaur, Parminder
Wang, Xuechun
Lin, Jiangguo
Lei, Xiaoying
White, Christian
You, Changjiang 
Wirth, Nicolas
Tessmer, Ingrid
Piehler, Jacob 
Riehn, Robert
Bishop, Alexander J. R.
Tao, Yizhi Jane
Wang, Hong
Stichwörter: ATOMIC-FORCE MICROSCOPY; Biochemistry & Molecular Biology; COMPLEX; GENE-EXPRESSION; HOMOLOGY-DIRECTED REPAIR; ONE-DIMENSIONAL DIFFUSION; QUANTUM-DOT; SACCHAROMYCES-CEREVISIAE; SISTER-CHROMATID COHESION; STRAND-BREAK REPAIR; TELOMERIC DNA
Erscheinungsdatum: 2018
Herausgeber: AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
Journal: JOURNAL OF BIOLOGICAL CHEMISTRY
Volumen: 293
Ausgabe: 3
Startseite: 1054
Seitenende: 1069
Zusammenfassung: 
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.
DOI: 10.1074/jbc.M117.806406

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