Biology subjects

Spanos, C.

Publications and source records attributed to Spanos, C..

At least 37 records · Page 2Linked to original sources

bioRxiv2024

Molecular basis for condensin enrichment at pericentromeres

Faithful chromosome segregation requires packaging of the genome on both global and local scales. Condensin plays a crucial role at pericentromeres to resist spindle forces and ensure the bioriented attachment of kinetochores to microtubules in mitosis. Here we demonstrate that budding yeast condensin is recruited to pericentromeres through a direct interaction between its Ycg1 subunit and the pericentromeric adaptor protein, shugoshin (Sgo1). We identify a Short Linear Motif (SLiM), termed CR1, within the C-terminal region of Sgo1 which inserts into a conserved pocket on Ycg1. Disruption of this interface abolishes the Sgo1-condensin interaction, prevents condensin recruitment to pericentromeres and results in defective sister kinetochore biorientation in mitosis. Similar motifs to CR1 are found in known and potential condensin binding partners and the Ycg1 binding pocket is broadly conserved, including in the mammalian homolog CAP-G. Overall, we uncover the molecular mechanism that targets condensin to define a specialized chromosomal domain.

cell biology↗

bioRxiv2024

Checkpoint-independent association of Mad3BUBR1 with Stu1CLASP directs homolog alignment in meiosis I

Gametes are produced via meiosis, a specialized cell division associated with frequent errors which cause birth defects and infertility. Uniquely in meiosis I, homologous chromosomes segregate to opposite poles, usually requiring their linkage by chiasmata, the products of crossover recombination1. The spindle checkpoint delays cell cycle progression until all chromosomes are properly attached to microtubules2 but the steps leading to the capture and alignment of chromosomes on the meiosis I spindle remain poorly understood. In budding yeast meiosis I, Mad2 and Mad3BUBR1 are equally important for spindle checkpoint delay, but biorientation of homologs on the meiosis I spindle requires Mad2, but not Mad3BUBR1 3,4. Here we show that Mad3BUBR1 promotes accurate meiosis I homolog segregation outside its canonical checkpoint role, independently of Mad2. We find that Mad3BUBR1 associates with the TOGL1 domain of Stu1CLASP, a conserved plus-end microtubule protein which is important for chromosome capture onto the spindle. Homologous chromosome pairs that are proficient in crossover formation, but which fail to biorient, rely on Mad3BUBR1-Stu1CLASP to ensure their efficient attachment to microtubules and segregation during meiosis I. Furthermore, we show that Mad3BUBR1-Stu1CLASP are essential to rescue the segregation of mini-chromosomes lacking crossovers. Our findings define a new pathway ensuring microtubule-dependent chromosome capture and demonstrate that spindle checkpoint proteins safeguard the fidelity of chromosome segregation both by actively promoting chromosome alignment and delaying cell cycle progression until this has occurred.

cell biology↗

bioRxiv2023

RNA 5' terminal nucleotide determines the strength of the RIG-I/IFN signaling pathway

The interferon (IFN) response is crucial for antiviral activity, but its overstimulation can lead to a wide range of autoimmune disorders. The cytoplasmic pattern recognition receptor RIG-I detects viral double-stranded RNAs (dsRNAs) and endogenous polymerase III transcripts carrying a 5'-triphosphate (5'-ppp) or 5'-diphosphate (5'-pp) moiety, triggering phosphorylation of IRF3 and IFN immune response. While many viral RNAs initiate with 5'-ppp-adenosine (5'-pppA) and most endogenous Pol III transcripts in higher eukaryotes start with 5'-ppp-guanosine (5'-pppG), no apparent reason for this bias has been identified so far. Here we demonstrate that dsRNAs initiating with 5'-pppA trigger stronger RIG-I/IFN response than those starting with 5'-pppG. We show that several GTP-binding proteins interact preferentially with 5'-pppG RNAs. Finally, supplementation with guanosine, but not adenosine, which rapidly increases intracellular concentrations of GTP and ATP, respectively, eliminates the difference in immunogenicity between 5'-pppG and 5'-pppA RNAs. Our findings suggest that 5'-pppG RNAs may enable certain RNA viruses and Pol III transcripts to limit detection by innate immune receptors. These results offer new insights into the sequence-dependent activation of the RIG-I/IFN pathway and have important implications for both antiviral immunity and the role of Pol III-derived RNAs in autoimmune diseases.

molecular biology↗

bioRxiv2023

Roles of SNORD115 and SNORD116 ncRNA clusters in neuronal differentiation

Prader-Willi syndrome shows features linked to brain development and hypothalamus-related endocrine abnormalities. The smallest clinical deletions fall within the large ([~]650Kb) SNHG14 gene, removing 29 consecutive introns that each generate SNORD116. SNHG14 also includes 48 tandem introns encoding SNORD115 and generates multiple, extended snoRNA-related species. SNORD115 and SNORD116 resemble box C/D small nucleolar RNAs (snoRNAs) but lack known targets. Both snoRNAs strongly accumulated during neuronal differentiation. SNORD116 accumulation apparently reflected stabilization, potentially linked to the appearance of FBLL1, a homologue of the ubiquitous snoRNA-associated protein Fibrillarin (FBL). In contrast, SNORD115 was selectively transcribed, apparently due to regulated termination. For functional characterization we created cell lines lacking only the expressed, paternal, SNORD115 or SNORD116 cluster. Analyses during neuronal development indicated changes in RNA stability and protein synthesis. Altered mRNAs included MAGEL2, mutation of which causes the PWS-like disorder Schaaf-Yang syndrome. Comparison of SNORD115 and SNORD116 mutants indicated overlapping or interacting functions. Most changes in mRNA and protein abundance appeared relatively late in development, with roles including cytoskeleton formation, extracellular matrix, neuronal arborization. Comparison with human embryonic midbrain development suggested enhanced progression in neuronal development in the snoRNA mutants. Subtle impairment of relative neuronal maturation during development, might generate the clinical phenotypes.

cell biology↗

bioRxiv2023

Rewiring of the phosphoproteome executes two meiotic divisions

The cell cycle is ordered by a controlled network of kinases and phosphatases. To generate gametes via meiosis, two distinct and sequential chromosome segregation events occur without an intervening S phase. How canonical cell cycle controls are modified for meiosis is not well understood. Here, using highly synchronous budding yeast populations, we reveal how the global proteome and phosphoproteome changes during the meiotic divisions. While protein abundance changes are limited to key cell cycle regulators, dynamic phosphorylation changes are pervasive. Our data indicate that two waves of cyclin-dependent kinase and Polo (Cdc5Polo) kinase activity drive successive meiotic divisions. These two distinct waves of phosphorylation are ensured by the meiosis-specific Spo13Meikin protein, which rewires the phosphoproteome. Spo13Meikin binds to Cdc5Polo to promote phosphorylation of a subset of substrates in meiosis I containing a newly identified motif, which we define as the Spo13Meikin -Cdc5Polo consensus phosphorylation motif. Overall, our findings reveal that a master regulator of meiosis redirects the activity of a kinase to change the phosphorylation landscape and elicit a developmental cascade.

cell biology↗

bioRxiv2023

Direct recruitment of Mis18 to interphase spindle poles promotes CENP-A chromatin assembly

CENP-A chromatin specifies mammalian centromere identity, and its chaperone HJURP replenishes CENP-A when recruited by the Mis18 complex (Mis18C) via M18BP/KNL2 to CENP-C at kinetochores during interphase. However, the Mis18C recruitment mechanism remains unresolved in species lacking M18BP1, such as fission yeast. Fission yeast centromeres cluster at G2 spindle pole bodies (SPBs) when CENP-ACnp1 is replenished and where Mis18C also localizes. We show that SPBs play an unexpected role in concentrating Mis18C near centromeres through the recruitment of Mis18 by direct binding to the major SPB LInker of Nucleoskeleton and Cytoskeleton (LINC) complex component Sad1. Mis18 recruitment by Sad1 is important for CENP-ACnp1 chromatin establishment and acts in parallel with a CENP-C-mediated Mis18C recruitment pathway to maintain centromeric CENP-ACnp1, but is independent of Sad1-mediated centromere clustering. SPBs therefore provide a non-chromosomal scaffold for both Mis18C recruitment and centromere clustering during G2. This centromere-independent Mis18-SPB recruitment provides a mechanism that governs de novo CENP-ACnp1 chromatin assembly by the proximity of appropriate sequences to SPBs and highlights how nuclear spatial organization influences centromere identity.

cell biology↗

bioRxiv2023

Improved detection and quantitation of RNA-interactomes using DIA SILAC

The RNA-interacting proteome is commonly characterized by UV-crosslinking followed by RNA purification, with protein recovery quantified using SILAC labeling followed by data-dependent acquisition (DDA) of proteomic data. However, the low efficiency of UV-crosslinking, combined with limited sensitivity of the DDA approach often restricts detection to relatively abundant proteins, necessitating multiple mass spec injections of fractionated peptides for each biological sample. Here we report an application of data-independent acquisition (DIA) with SILAC in a total RNA-associated protein purification (TRAPP) UV-crosslinking experiment. This gave 15% greater protein detection and lower inter-replicate variation relative to the same biological materials analyzed using DDA, while allowing single-shot analysis of the sample. As proof of concept, we determined the effects of arsenite treatment on the RNA-bound proteome of HEK293T cells. The DIA dataset yielded similar GO term enrichment for RNA-binding proteins involved in cellular stress responses to the DDA dataset while detecting extra proteins unseen by DDA. Overall, the DIA SILAC approach improved detection of proteins over conventional DDA SILAC for generating RNA-interactome datasets, at a lower cost due to reduced machine time.

molecular biology↗

bioRxiv2023

Ki-67 is necessary during DNA replication for forks protection and genome stability

BackgroundThe proliferation antigen Ki-67 has been widely used in clinical settings for cancer staging for many years but investigations on its biological functions have lagged. Recently, Ki-67 was shown to regulate both the composition of the chromosome periphery and chromosome behaviour in mitosis as well as to play a role in heterochromatin organisation and gene transcription. However, a role for Ki-67 in regulating cell cycle progression has never been reported. The progress towards understanding Ki-67 function have been limited by the tools available to deplete the protein coupled to its abundance and fluctuation during the cell cycle. ResultsHere we have used an auxin-inducible degron tag (AID) to achieve a rapid and homogeneous degradation of Ki-67 in HCT116 cells. This system, coupled with APEX2 proteomics and phospho-proteomics approaches, allowed us to show for the first time that Ki-67 plays a role during DNA replication. In its absence, DNA replication is severely delayed, the replication machinery is unloaded, causing DNA damage that is not sensed by the canonical pathways and dependant on HUWE1 ligase. This leads to replication and sister chromatids cohesion defects, but it also triggers an interferon response mediated by the cGAS/STING pathway in all the cell lines tested. ConclusionsWe have unveiled a new function of Ki-67 in DNA replication and genome maintenance that is independent of its previously known role in mitosis and gene regulation.

cell biology↗

bioRxiv2023

mps1 and mad mutations reduce Cryptococcus neoformans titan cell viability

Cryptococcus neoformans is an opportunistic, human fungal pathogen which undergoes fascinating switches in cell cycle control and ploidy when it encounters stressful environments such as the human lung. Here we carry out a mechanistic analysis of the spindle assembly checkpoint (SAC) which regulates the metaphase to anaphase transition, focusing on Mps1 kinase and the downstream checkpoint components Mad1 and Mad2. We demonstrate that Cryptococcus mad1{Delta} or mad2{Delta} strains are unable to respond to microtubule perturbations, continuing to re-bud and divide, and die rapidly as a consequence. Fluorescent tagging of Chromosome 3, using a lacO array and mNeonGreen-lacI fusion protein, demonstrates that mad mutants are unable to maintain sister-chromatid cohesion in the absence of microtubule polymers. Thus, the classic checkpoint functions of the SAC are conserved in Cryptococcus. In interphase, GFP-Mad1 is enriched at the nuclear periphery, and it is recruited to unattached kinetochores in mitosis. Purification of GFP-Mad1 followed by mass spectrometric analysis of associated proteins show that that it forms a complex with Mad2 and that it interacts with other checkpoint signalling components (Bub1) and effectors (Cdc20 and APC/C sub-units) in mitosis. We also demonstrate that overexpression of Mps1 kinase is sufficient to arrest Cryptococcus cells in mitosis, and show that this arrest is dependent on both Mad1 and Mad2. We find that a C-terminal fragment of Mad1 is an effective in vitro substrate for Mps1 kinase and map several Mad1 phosphorylation sites. Some sites are highly conserved within the C-terminal Mad1 structure and we demonstrate that mutation of threonine 667 (T667A) leads to loss of checkpoint signalling and abrogation of the GAL-MPS1 arrest. Thus Mps1-dependent phosphorylation of C-terminal Mad1 residues is a critical step in Cryptococcus spindle checkpoint signalling. Finally, we analyse the phenotype of mad and mps1 mutants during titan cell generation: quantitating viability of titan cells and their daughters generated during the ensuing reductive division. The mad1{Delta}, mad2{Delta} and mps{Delta} mutants show significantly reduced viability: many titans are dead and others produce slow growing colonies. We propose that these Cryptococcus neoformans checkpoint proteins have important roles in ensuring high fidelity chromosome segregation during stressful conditions, such that those heightened during its polyploid infection cycle.

cell biology↗

bioRxiv2022

SUMOylation regulates Lem2 function in centromere clustering and silencing

Regulation by the small modifier SUMO is heavily dependent on spatial control of enzymes that mediate the attachment and removal of SUMO on substrate proteins. Here we show that in fission yeast, delocalisation of the SUMO protease Ulp1 from the nuclear envelope results in centromeric defects that can be attributed to hyper-SUMOylation at the nuclear periphery. Unexpectedly, we find that while this localised hyper-SUMOylation impairs centromeric silencing, it can also enhance centromere clustering. Moreover, both effects are at least partially dependent on SUMOylation of the inner nuclear membrane protein Lem2. Lem2 has previously been implicated in diverse biological processes, including the promotion of both centromere clustering and silencing, but how these distinct activities are coordinated was unclear; our observations suggest a model whereby SUMOylation may serve as a regulatory switch, modulating Lem2 interactions with competing partner proteins to balance its roles in alternative pathways. Our findings also reveal a previously unappreciated role for SUMOylation in promoting centromere clustering.

cell biology↗

bioRxiv2022

Bub1 kinase acts as a signalling hub for the entire Cryptococcus neoformans spindle assembly checkpoint pathway

Cryptococcus neoformans (Cn) is an important human pathogen and a model system for basidiomycetes. Here we carry out a dissection of its spindle assembly checkpoint (SAC), focusing on Bub1 and Bub3. In many eukaryotes, including humans, Saccharomyces cerevisiae and Schizosaccharomyces pombe, Bub1 underwent gene duplication, generating paralogues referred to as Bub1 and BubR1 (or Mad3). Bub1 has upstream signalling functions at kinetochores, whilst BubR1/Mad3 is a component of the downstream mitotic checkpoint complex (MCC) that delays anaphase onset until all chromosomes are correctly attached. Here we demonstrate that the single CnBub1 protein carries out all the checkpoint roles of both Bub1 kinase and Mad3/BubR1. Proteomic analysis reveals kinetochore targeting via Spc105KNL1 and interactions with all downstream SAC components and effectors (Cdc20 and the anaphase promoting complex/cyclosome). We demonstrate that CnBub1 kinase activity is required to maintain prolonged checkpoint arrest. Thus CnBub1 acts as a SAC signalling hub and is a future target for anti-mitotic drugs.

cell biology↗

bioRxiv2022

DAXX adds a de novo H3.3K9me3 deposition pathway to the histone chaperone network

A multitude of histone chaperones are required to protect histones after their biosynthesis until DNA deposition. They cooperate through the formation of co-chaperone complexes, but the crosstalk between nucleosome assembly pathways remains enigmatic. Using explorative interactomics approaches, we characterize the organization of the histone H3-H4 chaperones network and define the interplay between histone chaperone systems. We identify and validate several novel histone dependent complexes and predict the structure of the ASF1 and SPT2 co-chaperone complex, expanding the role of ASF1 in histone dynamics. We show that DAXX acts separately from the rest of the network, recruiting heterochromatin factors and promoting lysine 9 tri-methylation of new histone H3.3 prior to deposition onto DNA. With its functionality, DAXX provides a molecular mechanism for de novo heterochromatin assembly. Collectively, our findings provide a new framework for understanding how cells orchestrate histone supply and comply with chromatin dynamics throughout the cell cycle.

molecular biology↗

bioRxiv2022

The SPARC complex defines RNAPII promoters in Trypanosoma brucei

Kinetoplastids are a highly divergent lineage of eukaryotes with unusual mechanisms for regulating gene expression. We previously surveyed 65 putative chromatin factors in the kinetoplastid Trypanosoma brucei. Our analyses revealed that the predicted histone methyltransferase SET27 and the Chromodomain protein CRD1 are tightly concentrated at RNAPII transcription start regions (TSRs). Here we report that SET27 and CRD1, together with four previously uncharacterized constituents, form the SET27 promoter-associated regulatory complex (SPARC), which is specifically enriched at TSRs. SET27 loss leads to aberrant RNAPII recruitment to promoter sites, accumulation of polyadenylated transcripts upstream of normal transcription start sites, and conversion of some normally unidirectional promoters to bidirectional promoters. Transcriptome analysis in the absence of SET27 revealed upregulated mRNA expression in the vicinity of SPARC peaks within the main body of chromosomes in addition to derepression of genes encoding variant surface glycoproteins (VSGs) located in subtelomeric regions. These analyses uncover a novel chromatin-associated complex required to establish accurate promoter position and directionality.

molecular biology↗

bioRxiv2022

Hypoxia shapes the immune landscape in lung injury promoting inflammation persistence

Acute Respiratory Distress Syndrome (ARDS), an often-fatal complication of pulmonary or systemic inflammation, has no cure. Hypoxemia is a defining feature, yet its impact on inflammation is often neglected. Patients with ARDS are monocytopenic early in the onset of the disease. Endotoxin or Streptococcus pneumoniae acute lung injury (ALI) in the context of hypoxia replicates this finding, through hypoxia-driven suppression of type I interferon signalling. This results in failed lung monocyte-derived interstitial macrophages (IM) niche expansion and unchecked neutrophilic inflammation. Administration of colony stimulating factor 1 (CSF1) rescues the monocytopenia, alters the circulating classical monocyte phenotype in hypoxic endotoxin-driven ALI and enables lung IM population expansion, thus limiting lung injury in endotoxin- and virally-induced hypoxic ALI. Hypoxia directly alters immune dynamics to the detriment of the host and manipulation of this aberrant response offers new therapeutic strategies for ARDS.

cell biology↗

bioRxiv2021

Proteasome-dependent truncation of the negative heterochromatin regulator Epe1 mediates antifungal resistance

Epe1 histone demethylase restricts H3K9-methylation-dependent heterochromatin, preventing it from spreading over, and silencing, gene-containing regions in fission yeast. External stress induces an adaptive response allowing heterochromatin island formation that confers resistance on surviving wild-type lineages. Here we investigate the mechanism by which Epe1 is regulated in response to stress. Exposure to caffeine or antifungals results in Epe1 ubiquitylation and proteasome-dependent removal of the N-terminal 150 residues from Epe1, generating truncated tEpe1 which accumulates in the cytoplasm. Constitutive tEpe1 expression increases H3K9 methylation over several chromosomal regions, reducing expression of underlying genes and enhancing resistance. Reciprocally, constitutive non- cleavable Epe1 expression decreases resistance. tEpe1-mediated resistance requires a functional JmjC demethylase domain. Moreover, caffeine-induced Epe1-to-tEpe1 cleavage is dependent on an intact cell-integrity MAP kinase stress signalling pathway, mutations in which alter resistance. Thus, environmental changes provoke a mechanism that curtails the function of this key epigenetic modifier, allowing heterochromatin to reprogram gene expression, thereby bestowing resistance to some cells within a population. H3K9me-heterochromatin components are conserved in human and crop plant fungal pathogens for which a limited number of antifungals exist. Our findings reveal how transient heterochromatin-dependent antifungal resistant epimutations develop and thus inform on how they might be countered.

cell biology↗

bioRxiv2021

The phospho-docking protein 14-3-3 regulates microtubule-associated proteins in oocytes including the chromosomal passenger Borealin

Global regulation of spindle-associated proteins is crucial in oocytes due to the absence of centrosomes and their very large cytoplasmic volume, but little is known about how this is achieved beyond involvement of the Ran-importin pathway. We previously uncovered a novel regulatory mechanism in Drosophila oocytes, in which the phospho-docking protein 14-3-3 suppresses microtubule binding of Kinesin-14/Ncd away from chromosomes. Here we report systematic identification of microtubule-associated proteins regulated by 14-3-3 from Drosophila oocytes. Proteins from ovary extract were co-sedimented with microtubules in the presence or absence of a 14-3-3 inhibitor. Through quantitative mass-spectrometry, we identified proteins or complexes whose ability to binding microtubules is suppressed by 14-3-3, including the chromosomal passenger complex (CPC), the centralspindlin complex and Kinesin-14/Ncd. We showed that 14-3-3 binds to the disordered region of Borealin, and this binding is regulated differentially by two phosphorylations on Borealin. Mutations at these two phospho-sites compromised normal Borealin localisation and centromere bi-orientation in oocytes, showing that phospho-regulation of 14-3-3 binding is important for Borealin localisation and function. The mass spectrometry data are available from ProteomeXchange, identifier . Author SummaryAccurate segregation of chromosomes during cell division is fundamental for genome stability. Chromosome segregation is mediated by the spindle, which is made of dynamic microtubules and associated proteins that regulate microtubule behaviour. How these microtubule-associated proteins are regulated is not well understood. Furthermore, as oocytes have an exceptionally large volume of cytoplasm and lack centrosomes, regulation of microtubule-associated proteins is especially crucial for organisation and function of the meiotic spindle. In this study, we showed that 14-3-3, a protein that binds to phosphorylated proteins, plays an important role to regulate multiple microtubule-associated proteins in fly oocytes. The regulated proteins include subunits of the conserved kinase complex called the chromosomal passenger complex. We further found that interaction of one of the subunits with 14-3-3 is regulated by two phosphorylations, and that these phosphorylations are important for localisation and function of this subunit. As these proteins are widely conserved including humans, this study may provide an insight into chromosome mis-segregation in human oocytes, which is very frequent and a major cause of human infertility, miscarriages and congenital birth conditions.

cell biology↗

bioRxiv2021

Mapping the invisible chromatin transactions of prophase chromosome remodelling

We have used a combination of chemical genetics, chromatin proteomics and imaging to map the earliest chromatin transactions during vertebrate cell entry into mitosis. Chicken DT40 CDK1as cells undergo synchronous mitotic entry within 15 minutes following release from a 1NM-PP1-induced arrest in late G2. In addition to changes in chromatin association with nuclear pores and the nuclear envelope, earliest prophase is dominated by changes in the association of ribonucleoproteins with chromatin, particularly in the nucleolus, where pre-rRNA processing factors leave chromatin significantly before RNA polymerase I. Nuclear envelope barrier function is lost early in prophase and cytoplasmic proteins begin to accumulate on the chromatin. As a result, outer kinetochore assembly appears complete by nuclear envelope breakdown (NEBD). Most interphase chromatin proteins remain associated with chromatin until NEBD, after which their levels drop sharply. An interactive proteomic map of chromatin transactions during mitotic entry is available as a resource at https://mitoChEP.bio.ed.ac.uk.

cell biology↗

bioRxiv2021

A disease-linked lncRNA mutation in RNase MRP inhibits ribosome synthesis

RMRP encodes a non-coding RNA forming the core of the RNase MRP ribonucleoprotein complex. Mutations cause Cartilage Hair Hypoplasia (CHH), characterized by skeletal abnormalities and impaired T cell activation. Yeast RNase MRP cleaves a specific site in the pre-ribosomal RNA (pre-rRNA) during ribosome synthesis. CRISPR-mediated disruption of RMRP in human cells lines caused growth arrest, with pre-rRNA accumulation. Here, we analyzed disease-relevant primary cells, showing that mutations in RMRP impair mouse T cell activation and delay pre-rRNA processing. Patient-derived human fibroblasts with CHH-linked mutations showed similar pre-rRNA processing delay. Human cells engineered with the most common CHH mutation (70AG in RMRP) show specifically impaired pre-rRNA processing, resulting in reduced mature rRNA and a reduced ratio of cytosolic to mitochondrial ribosomes. Moreover, the 70AG mutation caused a reduction in intact RNase MRP complexes. Together, these results indicate that CHH is a ribosomopathy, and the first processing-specific human disorder to be described. HighlightsO_LIMutations in RMRP lncRNA impair pre-rRNA processing and T cell activation C_LIO_LIPatient derived fibroblasts show impaired pre-rRNA processing C_LIO_LICells with the most common disease-linked mutation have specific processing defects C_LIO_LICytoplasmic ribosomes and intact RNase MRP complexes are also reduced in these cells C_LI

cell biology↗