An Alu element is a short stretch of DNA originally characterized by the action of the "Arthrobacter luteus (Alu)" restriction endonuclease. "Alu" elements are the most abundant transposable elements, containing over one million copies dispersed throughout the human genome. "Alu" elements were thought to be selfish or parasitic DNA, because their sole known function is self reproduction. However they are likely to play a role in evolution and have been used as genetic markers. They are derived from the small cytoplasmic 7SL RNA, a component of the signal recognition particle. "Alu" elements are highly conserved within primate genomes and originated in the genome of an ancestor of Supraprimates.