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Arrested replication forks guide retrotransposon integration

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Science  25 Sep 2015:
Vol. 349, Issue 6255, pp. 1549-1553
DOI: 10.1126/science.aaa3810

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Parasitic DNA targets a genomic home

Long-terminal-repeat (LTR) retrotransposons are a form of parasitic DNA that can jump around within the host's genome. To avoid damaging resident genes, they have been selected to integrate away from protein-coding sequences. For instance, the fission yeast LTR retrotransposon Tf1 inserts at nucleosome-free regions in gene promoters. Jacobs et al. show that Tf1 is directed to these insertion sites by a specific DNA binding protein, Sap1, which forms DNA replication–fork barriers.

Science, this issue p. 1549

Abstract

Long terminal repeat (LTR) retrotransposons are an abundant class of genomic parasites that replicate by insertion of new copies into the host genome. Fungal LTR retrotransposons prevent mutagenic insertions through diverse targeting mechanisms that avoid coding sequences, but conserved principles guiding their target site selection have not been established. Here, we show that insertion of the fission yeast LTR retrotransposon Tf1 is guided by the DNA binding protein Sap1 and that the efficiency and location of the targeting depend on the activity of Sap1 as a replication fork barrier. We propose that Sap1 and the fork arrest it causes guide insertion of Tf1 by tethering the integration complex to target sites.

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