Figure 2

Distribution of dinucleotide exclusion zones. Shown is the distribution of dinucleotide exclusion zones (mod-EZ) upstream of 49,876 human exons (having excluded cases in which the intron was less that 350 nucleotides). Y-axis: log [number of exons]. X-axis: log [size of mod-EZ]. Data are normalized to give a probability density function, which gives the probability that an exon chosen at random will have an exclusion zone of a given size; the area under each curve is 1. Blue lines: first exclusion zone (mod-EZ₁), measured from -25 (relative to the 3' splice site) to the first upstream occurrence of the particular dinucleotide (see Materials and methods). Red lines: second exclusion zone (mod-EZ₂), measured from -25 relative to the end of the mod-EZ₁. AG shows the largest variance between mod-EZ₁ and mod-EZ₂. Data was sorted into bins of logarithmically increasing widths rendered discrete (bin width 10 at ~100; bin width 100 at ~1,000), with final bin counts divided by bin width and by the total number of exons, followed by application of a three-point averaging filter to produce the given plots. See Materials and methods for full details.