FIGURE 9.
Backsplices are flanked by paired ALU elements and long introns. (A) The highest information-bearing motif discovered within 200 bp upstream of and downstream from backsplice locations shows high homology to ALU elements. Frequency of RepeatMasker-annotated ALU elements in flanking sequences 50, 100, 200, and 500 bp (B) upstream of or (C) downstream from these expression categories of backsplice events, as compared to control splice sites of expressed genes. (D) The frequency of complementing and noncomplementing ALU pairs located on opposite sides of a backsplice within a flank. (E) Annotated length of introns flanking backsplices as compared to introns flanking control exons generally. (*) P < 10−5, (**) P < 10−10, (***) P < 10−20.