Summary of poly(A) sites and tandem 3′ UTR genes. (A) Genomic locations of poly(A) sites. Only poly(A) sites with at least five normalized reads are considered. (B) Position-specific distributions of the canonical poly(A) signal hexamer AAUAAA for poly(A) sites from various genomic locations. (C) Schematics of tandem 3′ UTRs. (D) Examples of tandem-UTR genes with two, three, and seven 3′ UTR isoforms. (E) Number of genes with different numbers of tandem poly(A) sites and the comparison with Ensembl annotation. (F) Fraction of genes with the total frequency of minor 3′ UTR isoforms exceeding given thresholds (0.1%, 1%, 2%, 5%, 10%, 15%, and 20%). Frequencies of minor isoforms are calculated as one minus the top isoform frequency for genes with 2+ poly(A) sites (blue bars), and as one minus the sum of the frequencies of the top two isoforms for genes with 3+ poly(A) sites (red bars).
