Figure 2.

Mechanisms of AS. A three-exon pre-mRNA with two intronic regions (in the example) could be spliced into a mature mRNA through recognition of constitutive splice sites and removal of intronic regions. Otherwise, exon 2 is lost through exon skipping or intron 2 may be included in the mature RNA through intron retention. Alternatively, pieces of exon 1 or exon 2 may be lost when the spliceosome recognizes, respectively, alternative 5′ss or 3′ss. Altogether these mechanisms affect mRNA sequence and, consequently, the expression, localization, and function of the protein.