Intronic poly(A) sites in human genes. (A) Schematic of poly(A) sites located in different types of exons, i.e., composite terminal exon, skipped terminal exon, and 3′-most exon. 5′ss indicates 5′ splice site; pA, poly(A) site. Exons are shown as boxes. Splicing is indicated by an angled line. (B) Distance between 5′ss and composite exon poly(A) sites. Median values are 295 nt, 355 nt, and 238 nt for poly(A) sites in the conserved set 1, conserved set 2, and nonconserved set, respectively. (C) Distance between 5′ss and skipped exon poly(A) sites. Median values are 3445 nt, 2997 nt, and 2320 nt for poly(A) sites in the conserved set 1, conserved set 2, and nonconserved set, respectively. As indicated, solid black lines are for poly(A) sites in the conserved set 1, dotted black lines are for poly(A) sites in the conserved set 2, and solid gray lines are for poly(A) sites in the nonconserved set.