Examples of mutations in specific Alu elements that may underlie the emergence of polyadenylation signals. In each alignment, the top bar shows positions 117–172 of the specific Alu sequence, the bottom bar shows the same positions along its family reference, and the middle bar shows positions that are identical (|) or different (:). The positions of significantly over-represented mutations are marked in red. The canonical polyadenylation signal formed by the mutations is marked in blue. This signal, as well dinucleotide CG positions, are marked with capital letters. The cleavage position is marked by a vertical dashed blue line. (A) An AluSz6 element (chr1:160289488-160289990(−)), member of the 134-EoG-Alu set. A C>A mutation in position 119 creates the canonical polyadenylation signal AATAAA. (B) An AluSx element (chr1:27001322-27001784(+)), member of the 134-EoG-Alu set. A C>T mutation in position 119 creates the canonical polyadenylation signal ATTAAA. (C) An AluSc element (chr6:149590912-149591403(+)), member of the 141-EoG-Alu set. A C>A mutation in position 128 creates the canonical polyadenylation signal AATAAA.