Figure 2.

Minimal length of inter-CDS regions doesn't increase with the age of the regions. Depending on the phylogenetic distance to orthologous neighbouring gene pairs, we classified inter-CDS regions in S. cerevisiae into four age groups: 'young', 'plain old' (PO), 'very old' (VO), and 'extra old' (XO) (see Methods). (A) regions flanked by divergently transcribed genes; (B) regions flanked by uni-directionally transcribed genes; (C) regions flanked by convergently transcribed genes. The length distributions of all three 'old' age groups are very similar, except for the 'divergent' regions, where the relative weight shifts from the higher to the lower peak with increasing age.