1. European Bioinformatics Institute (EMBL-EBI), Wellcome Trust Genome Campus, Cambridge CB10 1SD, UK, and European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
2. National Technical University of Athens, Heroon Polytechniou 9, 15780 Zografou, Athens, Greece.
3. IBM Computational Biology Center, Yorktown Heights, NY 10598, USA.