Of the 1.1 million Alu retroposons in the human genome, about 10,000 are inserted in the 3' untranslated regions (UTR) of protein-coding genes and 1% of these (107 events) are active as polyadenylation sites (PASs). Strikingly, although Alu's in 3' UTR are indifferently inserted in the forward or reverse direction, 99% of polyadenylation-active Alu sequences are forward oriented. Consensus Alu+...