1. Biochemistry and Chemical Biology
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Imaging and energetics of single SSB-ssDNA molecules reveal intramolecular condensation and insight into RecOR function

  1. Jason C Bell
  2. Bian Liu
  3. Stephen C Kowalczykowski  Is a corresponding author
  1. University of California, Davis, United States
Research Article
  • Cited 19
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Cite this article as: eLife 2015;4:e08646 doi: 10.7554/eLife.08646


Escherichia coli single-stranded DNA (ssDNA) binding protein (SSB) is the defining bacterial member of ssDNA binding proteins essential for DNA maintenance. SSB binds ssDNA with a variable footprint of ~30-70 nucleotides, reflecting partial or full wrapping of ssDNA around a tetramer of SSB. We directly imaged single molecules of SSB-coated ssDNA using total internal reflection fluorescence (TIRF) microscopy and observed intramolecular condensation of nucleoprotein complexes exceeding expectations based on simple wrapping transitions. We further examined this unexpected property by single-molecule force spectroscopy using magnetic tweezers. In conditions favoring complete wrapping, SSB engages in long-range reversible intramolecular interactions resulting in condensation of the SSB-ssDNA complex. RecO and RecOR, which interact with SSB, further condensed the complex. Our data support the idea that RecOR--and possibly other SSB interacting proteins--function(s) in part to alter long-range, macroscopic interactions between or throughout nucleoprotein complexes by microscopically altering wrapping and bridging distant sites.

Article and author information

Author details

  1. Jason C Bell

    Graduate Group in Biochemistry and Molecular Biology, University of California, Davis, Davis, United States
    Competing interests
    No competing interests declared.
  2. Bian Liu

    Graduate Group in Biophysics, University of California, Davis, Davis, United States
    Competing interests
    No competing interests declared.
  3. Stephen C Kowalczykowski

    Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, United States
    For correspondence
    Competing interests
    Stephen C Kowalczykowski, Reviewing editor, eLife.

Reviewing Editor

  1. Michael R Botchan, University of California, Berkeley, United States

Publication history

  1. Received: May 11, 2015
  2. Accepted: September 18, 2015
  3. Accepted Manuscript published: September 18, 2015 (version 1)
  4. Version of Record published: November 25, 2015 (version 2)


© 2015, Bell et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.


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