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Silence. 2011 Jun 7;2:4. doi: 10.1186/1758-907X-2-4.

A 5'-uridine amplifies miRNA/miRNA* asymmetry in Drosophila by promoting RNA-induced silencing complex formation.

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Laboratoire de Biologie Moléculaire Eucaryote, 118 route de Narbonne, Université Toulouse III Paul Sabatier (UPS), F-31000 Toulouse, France.



MicroRNA (miRNA) are diverse in sequence and have a single known sequence bias: they tend to start with uridine (U).


Our analyses of fly, worm and mouse miRNA sequence data reveal that the 5'-U is recognized after miRNA production. Only one of the two strands can be assembled into Argonaute protein from a single miRNA/miRNA* molecule: in fly embryo lysate, a 5'-U promotes miRNA loading while decreasing the loading of the miRNA*.


We suggest that recognition of the 5'-U enhances Argonaute loading by a mechanism distinct from its contribution to weakening base pairing at the 5'-end of the prospective miRNA and, as recently proposed in Arabidopsis and in humans, that it improves miRNA precision by excluding incorrectly processed molecules bearing other 5'-nt.

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