Computer Laboratory, University of Cambridge, Cambridge CB3 0FD and Cambridge Systems Biology Centre, University of Cambridge, Cambridge CB2 1GA, UK.|Computer Laboratory, University of Cambridge, Cambridge CB3 0FD and Cambridge Systems Biology Centre, University of Cambridge, Cambridge CB2 1GA, UK.|Computer Laboratory, University of Cambridge, Cambridge CB3 0FD and Cambridge Systems Biology Centre, University of Cambridge, Cambridge CB2 1GA, UK.