title: Human let-7a miRNA blocks protein production on actively translating polyribosomes.
abstract: MicroRNAs (miRNAs) regulate gene expression at a post-transcriptional level through base-pairing to 3' untranslated regions (UTRs) of messenger RNAs. The mechanism by which human let-7a miRNA regulates mRNA translation was examined in HeLa cells expressing reporter mRNAs containing the Caenorhabditis elegans lin-41 3' UTR. let-7a miRNA strongly repressed translation, yet the majority of control and lin-41-bearing RNAs sedimented with polyribosomes in sucrose gradients; these polyribosomes, together with let-7a miRNA and the miRISC protein AGO, were released from those structures by puromycin. RNA containing the lin-41 3' UTR and an iron response element in the 5' UTR sedimented with polysomes when cells were incubated with iron, but showed ribosome run-off when the iron was chelated. These data indicate that let-7a miRNA inhibits actively translating polyribosomes. Nascent polypeptide coimmunoprecipitation experiments further suggest that let-7a miRNA interferes with the accumulation of growing polypeptides.
authors.affiliation: Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation St., Suite 204, Worcester, Massachusetts 01605, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Nottrott
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Simard
authors.forename: Joel D
authors.initials: JD
authors.lastname: Richter
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D006801:Humans; D035683:MicroRNAs / Q000235:genetics*; D018832:Molecular Chaperones / Q000378:metabolism; D011132:Polyribosomes / Q000235:genetics / Q000502:physiology*; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D012270:Ribosomes / Q000235:genetics
chemical_list: D035683:MicroRNAs; D018832:Molecular Chaperones; D012333:RNA, Messenger; C487931:mirnlet7 microRNA, human; C096099:nascent-polypeptide-associated complex