Institute of Structural and Molecular Biology, Division of Biosciences, University College London, Darwin Building, Gower Street, London WC1E 6BT. Contact:andrew@bioinf.org.uk -or- andrew.martin@ucl.ac.uk|Institute of Structural and Molecular Biology, Division of Biosciences, University College London, Darwin Building, Gower Street, London WC1E 6BT. Contact:andrew@bioinf.org.uk -or- andrew.martin@ucl.ac.uk|Institute of Structural and Molecular Biology, Division of Biosciences, University College London, Darwin Building, Gower Street, London WC1E 6BT. Contact:andrew@bioinf.org.uk -or- andrew.martin@ucl.ac.uk