Figure 1

The 29 exon categories in the POEM taxonomy. The vertical lines to the left indicate to which component(s) an exon belongs. The regions and CDS boundaries appear across the top of the diagram. The dashed vertical lines underneath "UT" and "TU" indicate the CDS boundaries. Each box or combination of adjacent white and shaded boxes represents one of the 29 exon categories. The translated region is darkened to aid visual demarcation from untranslated regions. An exon's moniker (or category name) is the combination of letters found within an exon. Dimension values are separated by periods (despite any CDS boundary). Lower case category names represent exons which can occur multiple times in the same protein coding gene; whereas all upper case monikers indicate exon categories that occur 0 or 1 times in a given protein coding gene. Space between two exon categories is to be understood as intronic. Place-holding exons are not displayed. Place-holding exons are those required by the taxonomical constraints to precede or follow a particular exon category. For example, internal exons (those whose monikers commence with an "I" or "i") can only exist if both preceded and followed by another exon.