The majority of endogenous microRNA targets within Alu elements avoid the microRNA machinery

The massive spread of repetitive elements in the human genome presents a substantial challenge to the organism, as such elements may accidentally contain seemingly functional motifs. A striking example is offered by the roughly one million copies of Alu repeats in the genome, of which ∼0.5% reside within genes' untranslated regions (UTRs), presenting ∼30 000 novel potential targets for highly conserved microRNAs (miRNAs). Here, we examine the functionality of miRNA targets within Alu elements in 3'UTRs in the human genome.