MOLECULAR BIOLOGY: Variety from Repetitive DNA

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Science  15 Aug 2008:
Vol. 321, Issue 5891, pp. 892a
DOI: 10.1126/science.321.5891.892a

Ionizing radiation is harmful to living creatures because it scythes through both strands of genomic DNA, leading to potentially lethal chromosome aberrations. To identify the origin of these aberrations, Argueso et al. have used x-rays to shred the genomes of diploid yeast cells and introduced a staggering ∼250 DNA breaks per cell; within 3 hours, most of the shattered chromosomes had been stitched together, with half of the analyzed surviving cells harboring at least one chromosome aberration. A molecular autopsy revealed that most aberrations were associated with a repetitive sequence, the Ty retrotransposon, a selfish DNA element scattered throughout the yeast genome, and that the aberrations appeared to have arisen via failed DNA repair attempts. Normally, homologous chromosomes in a diploid cell allow one chromosome to act as a template for the repair of the other. For breaks that occur in or near Ty elements, rather than the homologous element being used, any of the Ty elements in the yeast genome might be selected, mixing chromosomal material and making repetitive DNA a driving force for genomic variation. — GR

Proc. Natl. Acad. Sci. U.S.A. 105, 10.1073/pnas.0804529105 (2008).

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