FIGURE 3.

Influence of RNA polymerase II elongation rate on alternative splicing by “exon skipping.” Alternative splicing (top): when the 3′-splice site (SS) by the alternative exon is weaker than the 3′-SS of the downstream intron, low transcriptional elongation rates (right) favor exon inclusion, whereas high elongation rates (left) favor skipping. Constitutive splicing (bottom): when both 3′-SSs are strong, the exon is included constitutively independently of the elongation rate.