F. Box plot showing the distribution of fold enrichment values on series of introns of comparable size (4kb in average, ranging from 3 to 5kb) sorted by number of sense CACACA motifs per intron (2+, two or more motifs), n= 5782, 899, 960, and 3234 introns for all introns, 0, 1, and 2+ CACACA categories, respectively. R2, Linear regression coefficient between 0, 1, and 2+. Dashed line represents an IP/Input ratio of 1, taken as a reference. Data information: All box boundaries in Fig 4 represent 25th and 75th percentiles; center line represents median; whiskers indicate ±1.5×IQR; points are values of outliers. All P-values are * P < 0.01, ** P < 0.005, ***P < 0.001; two-tailed Student's t-test. 