1. Genome Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
2. European Molecular Biology Laboratory–European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SD, UK.
3. European Molecular Biology Laboratory–Hamburg Outstation c/o DESY, Notkestrasse 85, 22603 Hamburg, Germany.