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Dating back 65 million years, the AluJ lineage is the oldest and least active in the human genome. The younger AluS lineage is about 30 million years old and contains some active elements. Finally, the AluY elements are the youngest of the three and have the greatest disposition to retrotranspose along the human genome.

Alu elements successfully mobilize across the genome by interacting with signal recognition particles (SRPs), which aid newly translated proteins reach final destinations. Alu RNA forms a specific RNA/protein complex with an heterodimer consisting of named SRP9 and SRP14. SRP9/14 facilitates Alu's attachment to ribosomes that capture nascent L1 proteins. Thus, an Alu element can take control of the L1 protein's reverse transcriptase, ensuring that the Alu's mRNA sequence gets copied.