1. Control Group, Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K.
2. Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K.
3. Oxford Centre for Integrative Systems Biology, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K.