Computational Bioinformatics Laboratory, Department of Computer Science, Imperial College London, London, SW7 2BZ, UK. jcs06@doc.ic.ac.uk|Computational Bioinformatics Laboratory, Department of Computer Science, Imperial College London, London, SW7 2BZ, UK. jcs06@doc.ic.ac.uk|Computational Bioinformatics Laboratory, Department of Computer Science, Imperial College London, London, SW7 2BZ, UK. jcs06@doc.ic.ac.uk|Computational Bioinformatics Laboratory, Department of Computer Science, Imperial College London, London, SW7 2BZ, UK. jcs06@doc.ic.ac.uk|Computational Bioinformatics Laboratory, Department of Computer Science, Imperial College London, London, SW7 2BZ, UK. jcs06@doc.ic.ac.uk