Drosophila miR2 induces pseudo-polysomes and inhibits translation initiation.
MicroRNAs (miRs) inhibit protein synthesis by mechanisms that are as yet unresolved. We developed a cell-free system from Drosophila melanogaster embryos that faithfully recapitulates miR2-mediated translational control by means of the 3' untranslated region of the D. melanogaster reaper messenger RNA. Here we show that miR2 inhibits translation initiation without affecting mRNA stability. Surprisingly, miR2 induces the formation of dense (heavier than 80S) miRNPs ('pseudo-polysomes') even when polyribosome formation and 60S ribosomal subunit joining are blocked. An mRNA bearing an ApppG instead of an m7GpppG cap structure escapes the miR2-mediated translational block. These results directly show the inhibition of m7GpppG cap-mediated translation initiation as the mechanism of miR2 function, and uncover pseudo-polysomal messenger ribonucleoprotein assemblies that may help to explain earlier findings.
Thermann
Rolf
R
European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
Hentze
Matthias W
MW
D020413:3' Untranslated Regions / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D002474:Cell-Free System; D029721:Drosophila Proteins / Q000235:genetics; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics*; D017930:Genes, Reporter / Q000235:genetics; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism*; D011132:Polyribosomes / Q000235:genetics* / Q000378:metabolism*; D014176:Protein Biosynthesis; D012315:RNA Caps / Q000235:genetics / Q000378:metabolism; D020871:RNA Stability; D012261:Ribonucleoproteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D020413:3' Untranslated Regions; D029721:Drosophila Proteins; D035683:MicroRNAs; D012315:RNA Caps; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein; C086973:rpr protein, Drosophila