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Genetics, Vol. 168, 77-87, September 2004, Copyright © 2004
doi:10.1534/genetics.104.027003

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Abortive Transposition by a Group II Intron in Yeast Mitochondria

Lorna Dickson1, Stuart Connell, Hon-Ren Huang, R. Michael Henke2, Lu Liu and Philip S. Perlman3

Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9148

3 Corresponding author: Howard Hughes Medical Institute, 4000 Jones Bridge Rd., Chevy Chase, MD 20815.
E-mail: perlmanp{at}hhmi.org

Group II intron homing in yeast mitochondria is initiated at active target sites by activities of intron-encoded ribonucleoprotein (RNP) particles, but is completed by competing recombination and repair mechanisms. Intron aI1 transposes in haploid cells at low frequency to target sites in mtDNA that resemble the exon 1-exon 2 (E1/E2) homing site. This study investigates a system in which aI1 can transpose in crosses (i.e., in trans). Surprisingly, replacing an inefficient transposition site with an active E1/E2 site supports <1% transposition of aI1. Instead, the ectopic site was mainly converted to the related sequence in donor mtDNA in a process we call "abortive transposition." Efficient abortive events depend on sequences in both E1 and E2, suggesting that most events result from cleavage of the target site by the intron RNP particles, gapping, and recombinational repair using homologous sequences in donor mtDNA. A donor strain that lacks RT activity carries out little abortive transposition, indicating that cDNA synthesis actually promotes abortive events. We also infer that some intermediates abort by ejecting the intron RNA from the DNA target by forward splicing. These experiments provide new insights to group II intron transposition and homing mechanisms in yeast mitochondria.




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Multiple Fates of L1 Retrotransposition Intermediates in Cultured Human Cells
Mol. Cell. Biol., September 1, 2005; 25(17): 7780 - 7795.
[Abstract] [Full Text] [PDF]


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