title: Argonaute loading improves the 5' precision of both MicroRNAs and their miRNA* strands in flies.
abstract: MicroRNAs (miRNAs) are short regulatory RNAs that direct repression of their mRNA targets. The miRNA "seed"-nucleotides 2-7-establishes target specificity by mediating target binding. Accurate processing of the miRNA 5' end is thought to be under strong selective pressure because a shift by just one nucleotide in the 5' end of a miRNA alters its seed sequence, redefining its repertoire of targets (Figure 1). Animal miRNAs are produced by the sequential cleavage of partially double-stranded precursors by the RNase III endonucleases Drosha and Dicer, thereby generating a transitory double-stranded intermediate comprising the miRNA paired to its partially complementary miRNA* strand. Here, we report that in flies, the 5' ends of miRNAs and miRNA* strands are typically more precisely defined than their 3' ends. Surprisingly, the precision of the 5' ends of both miRNA and miRNA* sequences increases after Argonaute2 (Ago2) loading. Our data imply that either many miRNA* sequences are under evolutionary pressure to maintain their seed sequences-that is, they have targets-or that secondary constraints, such as the sequence requirements for loading small RNAs into functional Argonaute complexes, narrow the range of miRNA and miRNA 5' ends that accumulate in flies.
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.
authors.forename: Hervé
authors.initials: H
authors.lastname: Seitz
authors.forename: Megha
authors.initials: M
authors.lastname: Ghildiyal
authors.forename: Phillip D
authors.initials: PD
authors.lastname: Zamore
mesh_terms: D000818:Animals; D060565:Argonaute Proteins; D002460:Cell Line; D029721:Drosophila Proteins / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000378:metabolism*; D035683:MicroRNAs / Q000378:metabolism*; D034743:RNA-Induced Silencing Complex / Q000378:metabolism*; D043244:Ribonuclease III / Q000378:metabolism
chemical_list: C433807:AGO2 protein, Drosophila; D060565:Argonaute Proteins; D029721:Drosophila Proteins; D035683:MicroRNAs; D034743:RNA-Induced Silencing Complex; D043244:Ribonuclease III; C493335:drosha protein, Drosophila