Bioinformatics Unit, Department of Computer Science, University College London, Gower Street, London WC1E 6BT, UK.|Bioinformatics Unit, Department of Computer Science, University College London, Gower Street, London WC1E 6BT, UK.|Bioinformatics Unit, Department of Computer Science, University College London, Gower Street, London WC1E 6BT, UK.