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. 2019 Oct 25;8(1):61–72. doi: 10.1016/j.gendis.2019.10.011

Figure 1.

Figure 1

Four types of alternative polyadenylation events. (A) Tandem 3′UTR APA occurs within transcripts that possess two or more cleavage/poly(A) sites within their 3′ UTR, resulting in 3′UTR length differences between APA isoforms that code for identical gene products. (B) Alternative terminal exon APA is caused by alternative splicing, which results in internal exon skipping and use of a distinct poly(A) site contained within the new terminal exon. (C) Intronic APA involves the use of cryptic alternative poly(A) sites found within introns. (D) Internal exon APA features Poly(A) site usage within upstream exons, resulting in a truncated mRNA isoform lacking both a stop codon and a 3′UTR.