Likening his discovery to a paleontologist unearthing a new dinosaur species, Vladimir Kapitonov, a staff scientist at the Genetic Information Research Institute, recently revealed a new class of transposable elements in eukaryotes. These jumping genes use rolling circle replication--an ancient process characteristic of some plasmid replication in bacteria--to copy and insert itself throughout entire genomes (V.V. Kapitonov, J. Jurka, "Rolling circle transposons in eukaryotes," Proceedings of the National Academy of Sciences, 98[15]:8714-9 July 17, 2001.) Found in the genomes of Arabidopsis thaliana, Oriza sativa, and Caenorhabditis elegans, these elements have been dubbed helitrons because nearly always they code for a helicase, which unwinds the double helix at both the original transposon and the integration site. Through computational analysis of variation in transposons, which in Arabidopsis and nematodes constitute roughly 2 percent of genomic DNA, Kapitonov estimates that helitrons are tens of millions years old. The origin and...

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