Rcl1 Protein, a Novel Nuclease for 18 S Ribosomal RNA Production

Horn, Darryl; Mason, Sheila; Karbstein, Katrin

doi:10.1074/jbc.m111.268649

Cited by 71 publications

(80 citation statements)

References 27 publications

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“…4e), we had noticed that the cells accumulated 32S rRNA transcripts ( Supplementary Fig. 9d), indicating a defect in 32S cleavage at A 2 by the nucleolar SSU processome and associated factors 5,[38][39][40] . As such, we probed rRNA transcript processing in our anaphase-arrested cells (cdc15-2) depleted of Rio1 activity.…”

Section: Resultsmentioning

confidence: 99%

Rio1 promotes rDNA stability and downregulates RNA polymerase I to ensure rDNA segregation

et al. 2015

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The conserved protein kinase Rio1 localizes to the cytoplasm and nucleus of eukaryotic cells. While the roles of Rio1 in the cytoplasm are well characterized, its nuclear function remains unknown. Here we show that nuclear Rio1 promotes rDNA array stability and segregation in Saccharomyces cerevisiae. During rDNA replication in S phase, Rio1 downregulates RNA polymerase I (PolI) and recruits the histone deacetylase Sir2. Both interventions ensure rDNA copy-number homeostasis and prevent the formation of extrachromosomal rDNA circles, which are linked to accelerated ageing in yeast. During anaphase, Rio1 downregulates PolI by targeting its subunit Rpa43, causing PolI to dissociate from the rDNA. By stimulating the processing of PolI-generated transcripts at the rDNA, Rio1 allows for rDNA condensation and segregation in late anaphase. These events finalize the genome transmission process. We identify Rio1 as an essential nucleolar housekeeper that integrates rDNA replication and segregation with ribosome biogenesis. A t anaphase onset, the replicated chromosomes separate and then segregate along the mitotic spindle into the daughter cells. In the budding yeast Saccharomyces cerevisiae, the locus containing the genes that encode the ribosomal RNAs (rDNA) segregates after the rest of the genome, in late anaphase [1][2][3][4] . The rDNA locus exists as a tandem-repeat array comprising B150 rDNA units containing the 35S and 5S genes, which are transcribed by RNA polymerase I (PolI) and PolIII, respectively. Processing of the 35S pre-rRNA generates 5.8S, 18S and 25S rRNA that, together with the 5S rRNA, become the catalytic backbones of each ribosome 5,6 . Only in anaphase does yeast repress rDNA transcription 4 , which allows the sister rDNA loci to condensate and segregate. PolI downregulation in anaphase is mediated by the Cdc14 phosphatase acting on PolI subunit Rpa43 (ref. 4), resulting in PolI dissociating from the 35S rDNA. The removal of PolI and the local resolution of its transcripts allow the condensin complex to bind. The latter compacts the rDNA array and recruits the DNA decatenating enzyme topoisomerase II (refs 1,3,4,7) resulting in the physical separation and subsequent segregation of the sister rDNA loci.S. cerevisiae Rio1 belongs to the atypical RIO protein kinase family whose members lack the activation loop and substrate recognition domain present in canonical eukaryotic protein kinases [8][9][10][11] . Noteworthy, the RIO kinases may act especially as ATPases as they exhibit o0.1% kinase activity in vitro [12][13][14] . Cytoplasmic Rio1 contributes to pre-40S ribosome biogenesis by promoting 20S pre-rRNA maturation and by stimulating the recycling of trans-acting factors at the pre-40S subunit, both in yeast 12,[15][16][17][18] and human cells 19,20 . Roles in the nucleus are unknown for any RIO member, either in yeast or eukaryotes beyond. Using S. cerevisiae, we now describe the first activities of Rio1 in the nucleus. Foremost, Rio1 downregulates PolI transcription through the cell cycle. In G...

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Section: Resultsmentioning

confidence: 99%

Rio1 promotes rDNA stability and downregulates RNA polymerase I to ensure rDNA segregation

et al. 2015

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“…This PIN-domain endonuclease is positioned in proximity to the A 1 cleavage site [27,29,64] and cleaves a pre-rRNA substrate at site A 2 in vitro [64]. A second 90S-associated endonuclease with in vitro A 2 cleavage activity is Rcl1 [27,29,31,65]. Unfortunately, the positions of the rRNA segments around sites A 0 and A 2 could not be assigned in the current 90S structures [27,29].…”

Section: Dismantling Of the 90s Preribosome Releases An Early Pre-40smentioning

confidence: 96%

A Puzzle of Life: Crafting Ribosomal Subunits

Kressler

Hurt

Baßler

2017

Trends in Biochemical Sciences

164

127

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The biogenesis of eukaryotic ribosomes is a complicated process during which the transcription, modification, folding, and processing of the rRNA is coupled with the ordered assembly of $80 ribosomal proteins (r-proteins). Ribosome synthesis is catalyzed and coordinated by more than 200 biogenesis factors as the preribosomal subunits acquire maturity on their path from the nucleolus to the cytoplasm. Several biogenesis factors also interconnect the progression of ribosome assembly with quality control of important domains, ensuring that only functional subunits engage in translation. With the recent visualization of several assembly intermediates by cryoelectron microscopy (cryo-EM), a structural view of ribosome assembly begins to emerge. In this review we integrate these first structural insights into an updated overview of the consecutive ribosome assembly steps. Synopsis of Eukaryotic Ribosome AssemblyRibosomes are the molecular machines that translate the genetic information from the intermediary mRNA templates into proteins [1]. Eukaryotic 80S ribosomes comprise two unequal subunits that contain four different rRNAs and around 80 r-proteins ( Figure 1). The small 40S subunit (SSU) comprises the 18S rRNA and 33 r-proteins (referred to as RPS or S). The large 60S subunit (LSU) comprises the 25S/28S, 5.8S, and 5S rRNA and, in most eukaryotic species, 47 r-proteins (RPL or L); a notable exception is budding yeasts, which lack eL28The act of building a ribosome begins in the nucleolus, where the ribosomal DNA (rDNA) is transcribed into a long pre-rRNA precursor (35S pre-rRNA in yeast) and involves the ordered assembly of the r-proteins with the pre-rRNA, which is concomitantly processed into the mature rRNA species [5][6][7][8] (Figure 1 and Box 1). These assembly and processing events are tightly coupled and occur within preribosomal particles (see Glossary) that travel, as maturation progresses, from the nucleus across nuclear pore complexes (NPCs) to the cytoplasm, where they are ultimately converted into translation-competent ribosomal subunits [5,[9][10][11][12][13] (Figure 2, Key Figure). Given the gargantuan complexity of this process, it is unsurprising that the assembly of eukaryotic ribosomes strictly requires the assistance of a plethora (>200) of mostly essential ribosome biogenesis factors, which are also called trans-acting or assembly factors [5,14,15].Our current knowledge has been mainly obtained by studying ribosome biogenesis in the yeast Saccharomyces cerevisiae. Research conducted in the 1970s defined the r-protein composition of ribosomes, revealed the major pre-rRNA processing intermediates, and uncovered the existence of the 90S, 43S, and 66S preribosomal particles. The following 25 years witnessed the identification of numerous biogenesis factors and attributed functional roles TrendsCryoelectron microscopy analyses of the 90S preribosome show that the biogenesis factors create a casting mold that encloses the nascent pre-40S subunit.Structures of nuclear pre-60S particles reveal that a...

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“…Mutation of residues in the predicted active site in Utp24 caused reduced cell growth and defects in cleavage at the A 1 and A 2 sites, consistent with a role as the cleavage endonuclease for these steps in nucleolar SSU biogenesis. The cyclase-like protein, Rcl1, has also been proposed to be an endonuclease that cleaves at the A 2 site (Billy et al 2000;Horn et al 2011) as recombinant Rcl1 cleaves an rRNA fragment containing the A 2 site in vitro. However, extensive mutagenesis in the active site predicted by the crystal structure of the Kluyveromyces lactis Rcl1 revealed relative insensitivity to mutation (Tanaka et al 2011), although a triple mutation affects growth in vivo and A 2 cleavage in vitro (Horn et al 2011).…”

Section: Subcomplexes Are the Functional Units Of The Ssu Processomementioning

confidence: 99%

Ribosome Biogenesis in the YeastSaccharomyces cerevisiae

2013

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Ribosomes are highly conserved ribonucleoprotein nanomachines that translate information in the genome to create the proteome in all cells. In yeast these complex particles contain four RNAs (.5400 nucleotides) and 79 different proteins. During the past 25 years, studies in yeast have led the way to understanding how these molecules are assembled into ribosomes in vivo. Assembly begins with transcription of ribosomal RNA in the nucleolus, where the RNA then undergoes complex pathways of folding, coupled with nucleotide modification, removal of spacer sequences, and binding to ribosomal proteins. More than 200 assembly factors and 76 small nucleolar RNAs transiently associate with assembling ribosomes, to enable their accurate and efficient construction. Following export of preribosomes from the nucleus to the cytoplasm, they undergo final stages of maturation before entering the pool of functioning ribosomes. Elaborate mechanisms exist to monitor the formation of correct structural and functional neighborhoods within ribosomes and to destroy preribosomes that fail to assemble properly. Studies of yeast ribosome biogenesis provide useful models for ribosomopathies, diseases in humans that result from failure to properly assemble ribosomes. TABLE OF CONTENTS Abstract 643Introduction 644

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Rcl1 Protein, a Novel Nuclease for 18 S Ribosomal RNA Production

Cited by 71 publications

References 27 publications

Rio1 promotes rDNA stability and downregulates RNA polymerase I to ensure rDNA segregation

Rio1 promotes rDNA stability and downregulates RNA polymerase I to ensure rDNA segregation

A Puzzle of Life: Crafting Ribosomal Subunits

Ribosome Biogenesis in the YeastSaccharomyces cerevisiae

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