1. Centre for Biological Sciences, University of Southampton, Southampton SO16 7LB, U.K.
2. Department of Biochemistry and Molecular Biology and Centre for High-Throughput Biology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z3
3. AstraZeneca, Cancer and Infection Research Area, Discovery Bioscience, Mereside, Alderley Park, Macclesfield SK10 4TG, U.K.