Genome-wide target site triplication of Alu elements in the human
Wooseok Lee1, Seyoung Mun1,2, Keunsoo Kang3, Lothar Hennighausen2, and Kyudong
Department of Nanobiomedical Science & BK21 PLUS NBM Global Research Center for
Regenerative Medicine, Dankook University, Cheonan 330-714, Korea.
Laboratory of Genetics and Physiology, National Institute of Diabetes, Digestive and Kidney
Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Department of Microbiology, Dankook University, Cheonan 330-714, Korea.
DKU-Theragen institute for NGS analysis (DTiNa), Cheonan, 330-714, Republic of Korea.
Alu elements are the most successful short interspersed elements in primate genomes
and their retrotransposition is a major sources of genomic expansion. Alu elements integrate
into genomic regions through target-site primed reverse transcription, which generates target
site duplications (TSDs). Unexpectedly, we have identified target site triplications (TST) at
some loci, where two Alu elements in tandem share one direct repeat. Thus, the three copies
of the repeat are present. We located 214 TST loci in the human genome and examined 27
putative human-specific TST loci using PCR validation. As a result, 14 human-specific TST
loci were identified. These findings suggest that unequal homologous recombination between
TSDs can lead to TST. Through this mechanism, the copy number of Alu elements could
have increased in primate genomes without new Alu retrotransposition events. This study
provides new insight into the augmentation of Alu elements in the primate genome.