Frequent human genomic DNA transduction driven by LINE-1 retrotransposition

Human L1 retrotransposons can produce DNA transduction events in which unique DNA segments downstream of L1 elements are mobilized as part of aberrant retrotransposition events. That L1s are capable of carrying out such a reaction in tissue culture cells was elegantly demonstrated. Using bioinformatic approaches to analyze the structures of L1 element target site duplications and flanking sequence features, we provide evidence suggesting that ~ 15 % of full-length L1 elements bear evidence of flanking DNA segment transduction. Extrapolating these findings to the 600,000 copies of L1 in the genome, we predict that the amount of DNA transduced by L1 represents ~ 1 % of the genome, a fraction comparable with that occupied by exons. The LINE-1 (L1) retrotransposon family is estimated to contain 600,000 copies, accounting for at least 15 % of the human genomic DNA (Smit 1996). L1’s second ORF (ORF2) encodes endonuclease and reverse tran-scriptase activities (Mathias et al. 1991; Feng et al. 1996), and is the most abundant ORF in the genome. As a major source of reverse transcriptase, L1 is likely to be indirectly responsible for the spreading of other ret