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Nucleic Acids Res. 2017 Feb 28;45(4):1925-1945. doi: 10.1093/nar/gkw1366.

FACT is a sensor of DNA torsional stress in eukaryotic cells.

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Department of Cell Stress Biology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14127, USA.
Department of Evolutionary & Environmental Biology, Tauber Bioinformatics Research Center, University of Haifa, Mount Carmel, Haifa 31905, Israel.
Department of Chemical Carcinogenesis, Institute of Carcinogenesis, Blokhin Cancer Research Center RAMS, Moscow 115478, Russia.
I.P. Pavlov Ryazan State Medical University, Ryazan, Russia.
Department of Molecular Biology, Ariel University, Ariel 40700, Israel.
Department of Bioinformatics, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14127, USA.
Department of Molecular and Cell Biology, University of Texas at Dallas, 800 W. Campbell Rd., Richardson, TX 75080, USA.


Transitions of B-DNA to alternative DNA structures (ADS) can be triggered by negative torsional strain, which occurs during replication and transcription, and may lead to genomic instability. However, how ADS are recognized in cells is unclear. We found that the binding of candidate anticancer drug, curaxin, to cellular DNA results in uncoiling of nucleosomal DNA, accumulation of negative supercoiling and conversion of multiple regions of genomic DNA into left-handed Z-form. Histone chaperone FACT binds rapidly to the same regions via the SSRP1 subunit in curaxin-treated cells. In vitro binding of purified SSRP1 or its isolated CID domain to a methylated DNA fragment containing alternating purine/pyrimidines, which is prone to Z-DNA transition, is much stronger than to other types of DNA. We propose that FACT can recognize and bind Z-DNA or DNA in transition from a B to Z form. Binding of FACT to these genomic regions triggers a p53 response. Furthermore, FACT has been shown to bind to other types of ADS through a different structural domain, which also leads to p53 activation. Thus, we propose that FACT acts as a sensor of ADS formation in cells. Recognition of ADS by FACT followed by a p53 response may explain the role of FACT in DNA damage prevention.

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