Distribution of rate shifting sites per exon and along the exon. Mean rate shift abundance of “rate shifts to conservation” (A) and “rate shifts to variability” (B) are plotted for all examined constitutive (dark gray) and alternative (white) exons. Rate shift abundance was calculated as the mean number of rate shifting sites normalized per length. Constitutive exons have a lower conserved rate shift score and a lower variable rate shift score than alternative exons. Abundance of “rate shifts to conservation” (C) and “rate shifts to variability” (D) along exons are plotted for constitutive (Ci, Di) and alternative (Cii, Dii) exons. Each exon was divided into three regions (x-axis): 30 nt downstream from the 3′ss, middle of the exon, and 30 nt upstream of the 5′ss. Abundance of rate shifting sites in each of the regions are indicated (y-axis). Error bars represent the standard error of the mean.
