1. Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK.
2. Max-Planck-Institut für Biochemie, 82152, Martinsried, Germany.
3. Medical Research Council (MRC) Genome Damage and Stability Centre, University of Sussex, Brighton BN1 9RQ, UK.
4. Dunn School of Pathology, University of Oxford, Oxford OX1 3RF, UK.
5. MRC Laboratory of Molecular Biology, Cambridge, CB2 0QH, UK.