Untemplated Oligoadenylation Promotes Degradation of RISC-Cleaved Transcripts

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Science  22 Dec 2006:
Vol. 314, Issue 5807, pp. 1893
DOI: 10.1126/science.1135268

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Double-stranded RNA, processed to small interfering RNAs (siRNAs) by Dicer and incorporated into the RNA-induced silencing complex (RISC), triggers gene silencing by a variety of pathways in eukaryotes. RNA interference involving the degradation of homologous transcripts is the best-characterized mechanism. However, the fate of the RNA fragments resulting from siRNA-directed cleavage is poorly understood. We have identified a gene (MUT68) in the unicellular green alga Chlamydomonas reinhardtii that is required for the efficient decay of siRNA-targeted transcripts. MUT68 encodes a noncanonical polyadenylate polymerase that adds untemplated adenines to the 5′ RNA fragments after siRNA-mediated cleavage and appears to stimulate their exosome-dependent degradation.

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