24. Other mobile DNA in mammalian genomes
In primate genomes, a major SINE, the Alu element, maintains a prominent position. In the human genome, there are some 1.1 million Alus, accounting for about 11% of the genome mass. Alu elements evolved from 7SL RNA of the signal recognition particle. Alus are dimers of roughly 140 non-identical nucleotide monomers that are separated by an A-rich region. The left monomer contains an internal RNA polymerase III promoter composed of short A and B boxes. At the 3' end is a poly A tail, similar to that seen in the L1 and SVA elements. Alus acquired their name because these elements contain an Alu restriction endonuclease site.
Alus started to amplify in genomes about 65 million years ago and ...