Zhiping Weng1,2,3,4 and Roderic Guigó5,6 
1Bioinformatics Program, Boston University, Cummington Street, Boston, MA 02215, USA.
2Biomedical Engineering Department, Boston University, Cummington Street, Boston, MA 02215, USA.
3Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
4Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
5Center for Genomic Regulation, C/Dr. Aiguader 88, 08005 Barcelona, Spain.
6Research Group on BioMedical Informatics, Institut Municipal d'Investigació Mèdica, Universitat Pompeu Fabra, 08022 Barcelona, Spain.