1. Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK.
2. Department of Chemistry, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK.
3. Centre for Cutaneous Research, Institute of Cell and Molecular Science, Barts and The London Queen Mary's School of Medicine and Dentistry, 4, Newark Street, London, E1 2AT, UK.
4. Department of Photobiology, Guy's, King's and St Thomas' School of Medicine, St. John's Institute of Dermatology, King's College, London SE1 7EH, UK.
5. RIKEN Discovery Research Institute, Wako-shi, Saitama 351-0198 Japan.