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Panoramix enforces piRNA-dependent cotranscriptional silencing

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Science  16 Oct 2015:
Vol. 350, Issue 6258, pp. 339-342
DOI: 10.1126/science.aab0700

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A Gaulish partner in silencing transposons

Small noncoding piRNAs protect animal germline genomes from devastating mutation and rearrangement caused by transposons. In fruit fly ovaries, piRNAs bind to Piwi proteins, and together they are required for the recognition and silencing of these parasitic DNA elements. Yu et al. show that the gene Panoramix acts downstream of the piRNA-driven recognition of transposons to silence their transcription. Panoramix does this by binding newly synthesized transposon RNAs.

Science, this issue p. 339

Abstract

The Piwi-interacting RNA (piRNA) pathway is a small RNA–based innate immune system that defends germ cell genomes against transposons. In Drosophila ovaries, the nuclear Piwi protein is required for transcriptional silencing of transposons, though the precise mechanisms by which this occurs are unknown. Here we show that the CG9754 protein is a component of Piwi complexes that functions downstream of Piwi and its binding partner, Asterix, in transcriptional silencing. Enforced tethering of CG9754 to nascent messenger RNA transcripts causes cotranscriptional silencing of the source locus and the deposition of repressive chromatin marks. We have named CG9754 “Panoramix,” and we propose that this protein could act as an adaptor, scaffolding interactions between the piRNA pathway and the general silencing machinery that it recruits to enforce transcriptional repression.

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