Gene Function and Evolution, Bioinformatics and Genomics, Centre for Genomic Regulation (CRG), 08003 Barcelona, Spain and Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain Gene Function and Evolution, Bioinformatics and Genomics, Centre for Genomic Regulation (CRG), 08003 Barcelona, Spain and Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain.