MICHAEL M. COX is Professor of Biochemistry, University of Wisconsin-Madison, USA. His research focuses on recombinational DNA repair processes. In addition to the work on this text, Cox is a co-author of four editions of Lehninger Principles of Biochemistry. He has received awards for both his teaching and his research, including the 1989 Eli Lilly Award in Biological Chemistry, and two major teaching awards from the University of Wisconsin, USA, and the University of Wisconsin System. JENNIFER A. DOUDNA is Professor of Molecular and Cell Biology and Professor of Chemistry at the University of California, Berkeley, USA, and an Investigator of the Howard Hughes Medical Institute. She has received numerous awards for her research on RNA and RNA-protein structure and function, including the Johnson Foundation Prize for innovative research, the National Academy of Sciences Award for initiatives in research, the Alan T. Waterman Award from the National Science Foundation, and the Eli Lilly Award in Biological Chemistry from the American Chemical Society. MICHAEL O'DONNELL is at the Rockefeller University, USA. He is a member of the National Academy of Sciences.