Panoramix enforces piRNA-dependent cotranscriptional silencing

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