Nuclear export and cytoplasmic processing of precursors to the 40S ribosomal subunits in mammalian cells.
It is generally assumed that, in mammalian cells, preribosomal RNAs are entirely processed before nuclear exit. Here, we show that pre-40S particles exported to the cytoplasm in HeLa cells contain 18S rRNA extended at the 3' end with 20-30 nucleotides of the internal transcribed spacer 1. Maturation of this pre-18S rRNA (which we named 18S-E) involves a cytoplasmic protein, the human homolog of the yeast kinase Rio2p, and appears to be required for the translation competence of the 40S subunit. By tracking the nuclear exit of this precursor, we have identified the ribosomal protein Rps15 as a determinant of preribosomal nuclear export in human cells. Interestingly, inhibition of exportin Crm1/Xpo1 with leptomycin B strongly alters processing of the 5'-external transcribed spacer, upstream of nuclear export, and reveals a new cleavage site in this transcribed spacer. Completion of the maturation of the 18S rRNA in the cytoplasm, a feature thought to be unique to yeast, may prevent pre-40S particles from initiating translation with pre-mRNAs in eukaryotic cells. It also allows new strategies for the study of preribosomal transport in mammalian cells.
Rouquette
Jacques
J
Laboratoire de Biologie Moléculaire des Eucaryotes and Institut d'Exploration Fonctionnelle des Génomes, CNRS and Université Paul Sabatier, Toulouse cedex, France.
Choesmel
Valérie
V
Gleizes
Pierre-Emmanuel
PE
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D015152:Blotting, Northern; D002458:Cell Fractionation; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D017931:DNA Primers; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D028884:Karyopherins / Q000037:antagonists & inhibitors; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D034622:RNA Interference; D012322:RNA Precursors / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects / Q000502:physiology*; D034443:RNA Transport / Q000502:physiology*; D012337:RNA, Ribosomal, 18S / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors; D012269:Ribosomal Proteins; D000097606:Exportin 1 Protein
D017931:DNA Primers; D005231:Fatty Acids, Unsaturated; D049452:Green Fluorescent Proteins; D028884:Karyopherins; D009687:Nuclear Proteins; D012322:RNA Precursors; D012337:RNA, Ribosomal, 18S; D018160:Receptors, Cytoplasmic and Nuclear; D012269:Ribosomal Proteins; D000097606:Exportin 1 Protein; C069798:Rps15 protein, mouse; C485184:enhanced green fluorescent protein; C038753:leptomycin B