Center for Bioinformatics, Saarland University, Building E1 1, 66804 Saarbrücken, Germany. ack@bioinf.uni-sb.de|Center for Bioinformatics, Saarland University, Building E1 1, 66804 Saarbrücken, Germany. ack@bioinf.uni-sb.de|Center for Bioinformatics, Saarland University, Building E1 1, 66804 Saarbrücken, Germany. ack@bioinf.uni-sb.de