1. Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, 111 T. W. Alexander Drive, Research Triangle Park, North Carolina 27709, United States
2. Department of Therapeutic Radiology and Genetics, Yale University School of Medicine, New Haven, Connecticut 06520, United States
3. Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062, United States
4. Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-0371, United States