Interdisciplinary Centre for Bioinformatics, University of Leipzig, Haertelstrasse 16-18, D-04107 Leipzig, Germany. roman@bioinf.uni-leipzig.de|Interdisciplinary Centre for Bioinformatics, University of Leipzig, Haertelstrasse 16-18, D-04107 Leipzig, Germany. roman@bioinf.uni-leipzig.de|Interdisciplinary Centre for Bioinformatics, University of Leipzig, Haertelstrasse 16-18, D-04107 Leipzig, Germany. roman@bioinf.uni-leipzig.de|Interdisciplinary Centre for Bioinformatics, University of Leipzig, Haertelstrasse 16-18, D-04107 Leipzig, Germany. roman@bioinf.uni-leipzig.de