DNA Ligase IV Guides End-Processing Choice during Nonhomologous End Joining
Michael P. Conlin,
Dylan A. Reid,
George W. Small,
Howard H. Chang,
Go Watanabe,
Michael R. Lieber,
Dale A. Ramsden,
Eli Rothenberg
Affiliations
Michael P. Conlin
Lineberger Comprehensive Cancer Center, Curriculum in Genetics and Molecular Biology, and Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA
Dylan A. Reid
Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA
George W. Small
Lineberger Comprehensive Cancer Center, Curriculum in Genetics and Molecular Biology, and Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA
Howard H. Chang
University of Southern California Keck School of Medicine, Norris Comprehensive Cancer Center, Los Angeles, CA 90033, USA
Go Watanabe
University of Southern California Keck School of Medicine, Norris Comprehensive Cancer Center, Los Angeles, CA 90033, USA
Michael R. Lieber
University of Southern California Keck School of Medicine, Norris Comprehensive Cancer Center, Los Angeles, CA 90033, USA
Dale A. Ramsden
Lineberger Comprehensive Cancer Center, Curriculum in Genetics and Molecular Biology, and Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA
Eli Rothenberg
Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA
Nonhomologous end joining (NHEJ) must adapt to diverse end structures during repair of chromosome breaks. Here, we investigate the mechanistic basis for this flexibility. DNA ends are aligned in a paired-end complex (PEC) by Ku, XLF, XRCC4, and DNA ligase IV (LIG4); we show by single-molecule analysis how terminal mispairs lead to mobilization of ends within PECs and consequent sampling of more end-alignment configurations. This remodeling is essential for direct ligation of damaged and mispaired ends during cellular NHEJ, since remodeling and ligation of such ends both require a LIG4-specific structural motif, insert1. Insert1 is also required for PEC remodeling that enables nucleolytic processing when end structures block direct ligation. Accordingly, cells expressing LIG4 lacking insert1 are sensitive to ionizing radiation. Cellular NHEJ of diverse ends thus identifies the steps necessary for repair through LIG4-mediated sensing of differences in end structure and consequent dynamic remodeling of aligned ends.
