title: The G-patch protein NF-κB-repressing factor mediates the recruitment of the exonuclease XRN2 and activation of the RNA helicase DHX15 in human ribosome biogenesis.
abstract: In eukaryotes, the synthesis of ribosomal subunits, which involves the maturation of the ribosomal (r)RNAs and assembly of ribosomal proteins, requires the co-ordinated action of a plethora of ribosome biogenesis factors. Many of these cofactors remain to be characterized in human cells. Here, we demonstrate that the human G-patch protein NF-κB-repressing factor (NKRF) forms a pre-ribosomal subcomplex with the DEAH-box RNA helicase DHX15 and the 5΄-3΄ exonuclease XRN2. Using UV crosslinking and analysis of cDNA (CRAC), we reveal that NKRF binds to the transcribed spacer regions of the pre-rRNA transcript. Consistent with this, we find that depletion of NKRF, XRN2 or DHX15 impairs an early pre-rRNA cleavage step (A'). The catalytic activity of DHX15, which we demonstrate is stimulated by NKRF functioning as a cofactor, is required for efficient A' cleavage, suggesting that a structural remodelling event may facilitate processing at this site. In addition, we show that depletion of NKRF or XRN2 also leads to the accumulation of excised pre-rRNA spacer fragments and that NKRF is essential for recruitment of the exonuclease to nucleolar pre-ribosomal complexes. Our findings therefore reveal a novel pre-ribosomal subcomplex that plays distinct roles in the processing of pre-rRNAs and the turnover of excised spacer fragments.
authors.affiliation: Institute for Molecular Biology, University Medical Center Göttingen, Georg-August-University, 37073 Göttingen, Germany.
authors.forename: Indira
authors.initials: I
authors.lastname: Memet
authors.affiliation: Institute for Molecular Biology, University Medical Center Göttingen, Georg-August-University, 37073 Göttingen, Germany.
authors.forename: Carmen
authors.initials: C
authors.lastname: Doebele
authors.affiliation: Institute for Molecular Biology, University Medical Center Göttingen, Georg-August-University, 37073 Göttingen, Germany.
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Sloan
authors.affiliation: Institute for Molecular Biology, University Medical Center Göttingen, Georg-August-University, 37073 Göttingen, Germany.|Göttingen Centre for Molecular Biosciences, Georg-August-University, 37073 Göttingen, Germany.
authors.forename: Markus T
authors.initials: MT
authors.lastname: Bohnsack
mesh_terms: D055162:Biocatalysis; D002466:Cell Nucleolus / Q000378:metabolism; D004789:Enzyme Activation; D005095:Exoribonucleases / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D001678:Organelle Biogenesis; D011485:Protein Binding; D020365:RNA Helicases / Q000378:metabolism*; D012322:RNA Precursors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D054657:Ribosome Subunits / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*
chemical_list: C111027:NKRF protein, human; D012322:RNA Precursors; D012335:RNA, Ribosomal; D012097:Repressor Proteins; C539469:DHX15 protein, human; D005095:Exoribonucleases; C120903:XRN2 protein, human; D020365:RNA Helicases