Single-Molecule Visualization of Human BLM Helicase as it Acts Upon Double- and Single-Stranded DNA Substrates
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Date
2019-09
Authors
Xue, Chaoyou
Daley, James M.
Xue, Xiaoyu
Steinfeld, Justin
Kwon, Youngho
Sung, Patrick
Greene, Eric C.
Journal Title
Journal ISSN
Volume Title
Publisher
Oxford University Press
Abstract
Bloom helicase (BLM) and its orthologs are essential for the maintenance of genome integrity. BLM defects represent the underlying cause of Bloom Syndrome, a rare genetic disorder that is marked by strong cancer predisposition. BLM deficient cells accumulate extensive chromosomal aberrations stemming from dysfunctions in homologous recombination (HR). BLM participates in several HR stages and helps dismantle potentially harmful HR intermediates. However, much remains to be learned about the molecular mechanisms of these BLM-mediated regulatory effects. Here, we use DNA curtains to directly visualize the activity of BLM helicase on single molecules of DNA. Our data show that BLM is a robust helicase capable of rapidly (∼70-80 base pairs per second) unwinding extensive tracts (∼8-10 kilobases) of double-stranded DNA (dsDNA). Importantly, we find no evidence for BLM activity on single-stranded DNA (ssDNA) that is bound by replication protein A (RPA). Likewise, our results show that BLM can neither associate with nor translocate on ssDNA that is bound by the recombinase protein RAD51. Moreover, our data reveal that the presence of RAD51 also blocks BLM translocation on dsDNA substrates. We discuss our findings within the context of potential regulator roles for BLM helicase during DNA replication and repair.
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Keywords
bloom helicase, BLM, genome integrity, homologous recombination, Chemistry and Biochemistry
Citation
Xue, C., Daley, J. M., Xue, X., Steinfeld, J., Kwon, Y., Sung, P., & Greene, E. C. (2019). Single-molecule visualization of human BLM helicase as it acts upon double- and single-stranded DNA substrates. Nucleic Acids Research, 47(21), pp. 11225–11237.
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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.