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posted 14. May 2002 15:36
Nature Genetics: June 2002, 31:2, 159-165.
DNA repair mediated by endonuclease-independent LINE-1 retrotransposition
by Tammy A. Morrish, Nicolas Gilbert, Jeremy S. Myers, Bethaney J. Vincent, Thomas D. Stamato, Guillermo E. Taccioli, Mark A. Batzer & John V. Moran
Abstract-Long interspersed elements (LINE-1s) are abundant retrotransposons in mammalian genomes that probably retrotranspose by target site-primed reverse transcription (TPRT)1, 2. During TPRT, the LINE-1 endonuclease cleaves genomic DNA3, freeing a 3' hydroxyl that serves as a primer for reverse transcription of LINE-1 RNA by LINE-1 reverse transcriptase. The nascent LINE-1 cDNA joins to genomic DNA, generating LINE-1 structural hallmarks such as frequent 5' truncations, a 3' poly(A)+ tail and variable-length target site duplications (TSDs)2. Here we describe a pathway for LINE-1 retrotransposition in Chinese hamster ovary (CHO) cells that acts independently of endonuclease but is dependent upon reverse transcriptase. We show that endonuclease-independent LINE-1 retrotransposition occurs at near-wildtype levels in two mutant cell lines that are deficient in nonhomologous end-joining (NHEJ). Analysis of the pre- and post-integration sites revealed that endonuclease-independent retrotransposition results in unusual structures because the LINE-1s integrate at atypical target sequences, are truncated predominantly at their 3' ends and lack TSDs. Moreover, two of nine endonuclease-independent retrotranspositions contained cDNA fragments at their 3' ends that are probably derived from the reverse transcription of endogenous mRNA. Thus, our results suggest that LINE-1s can integrate into DNA lesions, resulting in retrotransposon-mediated DNA repair in mammalian cells.
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