Alu Elements

Alu elements have reached a copy number in excess of 1 x 106, representing more than 10% of the human genome (1). They are widely distributed across the entire genome, with only a relatively few regions that have few of them. Alu elements tend to be enriched in the GC-rich, gene-rich regions, with many Alu elements located in the introns of genes.

The current rate of Alu amplification has been estimated to be in the range of one new insertion per 20-200 human births (2,3). The Alu insertion process has the potential to damage the genome both through insertional mutagenesis, and through facilitation of unequal, homologous recombination events (2). Insertional mutagenesis by Alu causes approx

From: Genomic Disorders: The Genomic Basis of Disease Edited by: J. R. Lupski and P. Stankiewicz © Humana Press, Totowa, NJ

Fig. 1. Structure of anAlu element. A typicalAlu element is schematized with the arrowheads representing the short, direct repeats formed at the point of insertion. The left half ofAlu contains the A and B boxes of the RNA polymerase III promoter. The two halves of the Alu dimer are separated by an A-rich region and the 3' end of the Alu contains a variable, A-rich region. The line above represents a typical Alu transcript, which terminates in the downstream flanking sequence at a terminator that generally contains four or more T residues in a row. The dotted portion of the line represents sequences downstream of the Alu element that will be variable between transcripts from different genomic loci.

Fig. 1. Structure of anAlu element. A typicalAlu element is schematized with the arrowheads representing the short, direct repeats formed at the point of insertion. The left half ofAlu contains the A and B boxes of the RNA polymerase III promoter. The two halves of the Alu dimer are separated by an A-rich region and the 3' end of the Alu contains a variable, A-rich region. The line above represents a typical Alu transcript, which terminates in the downstream flanking sequence at a terminator that generally contains four or more T residues in a row. The dotted portion of the line represents sequences downstream of the Alu element that will be variable between transcripts from different genomic loci.

0.1% ofhuman genetic disease, whereas recombination processes contribute to a much higher level. Little is known about the influence of Alu insertions in somatic or transformed cells. They have the potential to contribute to genetic instability in tumorigenesis, aging, and other somatic disorders.

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