FIGURE 1.

The process and diverse patterns of AS. (A) The splicing process undergoes sequential phosphodiester transfer reactions, which is catalysed by spliceosomes, including five snRNPs U1, U2, U4, U5 and U6 as well as splicing factors. The snRNAs cooperate to recognise the splice sites and catalyse the two steps of splicing reaction. (B) The diverse patterns of AS include exon skipping, alternative 3′SS selection, alternative 5′SS selection, alternative first exon, alternative last exon, intron retention and mutually exclusive exons.