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Science 25 August 2006:
Vol. 313. no. 5790, p. 1016
DOI: 10.1126/science.313.5790.1016n
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RNA interference (RNAi) targets sequences to be silenced through complementary small interfering (si)RNAs. SiRNAs are bound by Ago proteins, some of which can "slice" and inactivate target RNAs. RNAi silences gene expression at both the posttranscriptional and transcriptional levels. In posttranscriptional gene silencing, siRNAs target messenger RNAs. The target of siRNAs in transcriptional gene silencing (TGS) could be either DNA or the RNA generated from it. Irvine et al. (p. 1134) made mutations in the lone fission yeast Ago protein that prevent it from slicing. The mutant protein has a greatly diminished TGS activity, suggesting that siRNAs interact with nascent RNA rather than the DNA that encodes it to extinguish transcription. Furthermore, spreading of TGS to neighboring genes requires read-through transcription of the targeted and sliced nascent transcripts.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)