A Flexible Interface between DNA Ligase and PCNA Supports Conformational Switching and Efficient Ligation of DNA

John M. Pascal, Oleg V. Tsodikov, Greg L. Hura, Wei Song, Elizabeth A. Cotner, Scott Classen, Alan E. Tomkinson, John A. Tainer, Tom Ellenberger

Research output: Contribution to journalArticlepeer-review

138 Scopus citations


DNA sliding clamps encircle DNA and provide binding sites for many DNA-processing enzymes. However, it is largely unknown how sliding clamps like proliferating cell nuclear antigen (PCNA) coordinate multistep DNA transactions. We have determined structures of Sulfolobus solfataricus DNA ligase and heterotrimeric PCNA separately by X-ray diffraction and in complex by small-angle X-ray scattering (SAXS). Three distinct PCNA subunits assemble into a protein ring resembling the homotrimeric PCNA of humans but with three unique protein-binding sites. In the absence of nicked DNA, the Sulfolobus solfataricus DNA ligase has an open, extended conformation. When complexed with heterotrimeric PCNA, the DNA ligase binds to the PCNA3 subunit and ligase retains an open, extended conformation. A closed, ring-shaped conformation of ligase catalyzes a DNA end-joining reaction that is strongly stimulated by PCNA. This open-to-closed switch in the conformation of DNA ligase is accommodated by a malleable interface with PCNA that serves as an efficient platform for DNA ligation.

Original languageEnglish
Pages (from-to)279-291
Number of pages13
JournalMolecular Cell
Issue number2
StatePublished - Oct 20 2006

Bibliographical note

Funding Information:
We thank the beamline staff at ALS-SIBYLS for help with experiments, and we thank members of our laboratories for thoughtful discussion. This work was supported by a grant from the National Institute of General Medical Sciences (GM52504 to T.E.), by National Cancer Institute grants (CA081967 to J.A.T.), and by program P01 CA92584 (to J.A.T., A.E.T., and T.E.). We thank the U.S. Department of Energy for support of the SIBYLS beamline and of SAXS experiments under contract number DE-AC02-05CH11231.


  • DNA

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


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