Cross-species mapping of human bidirectional promoters. (A) The 1,585 protein-coding gene pairs are represented as 3,170 individual genes for clarity of the analysis. These genes were mapped to the mouse genome to identify the presence of orthologous bidirectional promoters. If the mouse annotations independently supported a bidirectional promoter at the orthologous location, and the genes on each side of the mouse promoter were shown to be orthologs of the human gene pair, then promoter orthology was confirmed. The annotations in the mouse included the mouse Known Gene (mm10_KG) where no more than 1,000 bp separated the transcription start sites in mouse as well as in human. Results using an unlimited distance between the genes in mouse are shown in the panel mm10_KG_NoLimit. A composite dataset of the mouse Known Genes and mouse ESTs occupies the lower panel, MM10_KG_spEST. (B) The 2,939 gene pairs represented by 5,878 individual genes in the human spliced ESTs were mapped to the mouse genome to identify the orthologous bidirectional promoters. The three panels use the same validation approach as in panel A, shown by the same labels.