DNA repair mediated by endonuclease-independent LINE-1 retrotransposition.
Long interspersed elements (LINE-1s) are abundant retrotransposons in mammalian genomes that probably retrotranspose by target site-primed reverse transcription (TPRT). During TPRT, the LINE-1 endonuclease cleaves genomic DNA, 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). 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.
Morrish
Tammy A
TA
Department of Human Genetics, University of Michigan Medical School, 1241 E. Catherine Street, Ann Arbor, Michigan 48105-0618, USA.
Gilbert
Nicolas
N
Myers
Jeremy S
JS
Vincent
Bethaney J
BJ
Stamato
Thomas D
TD
Taccioli
Guillermo E
GE
Batzer
Mark A
MA
Moran
John V
JV
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004260:DNA Repair / Q000235:genetics / Q000502:physiology*; D006801:Humans; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D018626:Retroelements / Q000235:genetics / Q000502:physiology*
D018626:Retroelements