Alu Elements

Definition

The most abundant class of dispersed repeat elements in the human genome, and one member of the family of short interspersed repeat elements (SINEs). An estimated one million copies comprise about 10% of DNA in human cells.

Characteristics

Structure

Alu elements are 280 bp in length, and consist of two similar monomers that have homology to, and were originally derived from, the 7SL RNA gene (Fig. 1). Individual Alu elements are flanked by direct repeats, end in a 3′ A-rich tract, and the left monomer contains an internal RNA polymerase III promoter which directs transcription initiation to the first residue of the element. Alu are retrotransposable elements, and several subfamilies, mobilized from different “source” genes at different evolutionary times, can be recognized on the basis of their sequence divergence and diagnostic bases. Some of the more recently integrated subfamilies are polymorphic, occupying regions on some chromosomes that are not occupied