scholarly journals Unraveling the stepwise maturation of the yeast telomerase including a Cse1 and Mtr10 mediated quality control checkpoint

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Anna Greta Hirsch ◽  
Daniel Becker ◽  
Jan-Philipp Lamping ◽  
Heike Krebber
Keyword(s):  
Quality Control ◽  
Nuclear Import ◽  
Model Organism ◽  
Reverse Transcriptase Activity ◽  
Yeast Telomerase ◽  
Control Step ◽  
Nuclear Exosome ◽  
Transport Factors ◽  
Cell Immortality ◽  
Chromosome Regions

AbstractTelomerases elongate the ends of chromosomes required for cell immortality through their reverse transcriptase activity. By using the model organism Saccharomyces cerevisiae we defined the order in which the holoenzyme matures. First, a longer precursor of the telomerase RNA, TLC1 is transcribed and exported into the cytoplasm, where it associates with the protecting Sm-ring, the Est and the Pop proteins. This partly matured telomerase is re-imported into the nucleus via Mtr10 and a novel TLC1-import factor, the karyopherin Cse1. Remarkably, while mutations in all known transport factors result in short telomere ends, mutation in CSE1 leads to the amplification of Y′ elements in the terminal chromosome regions and thus elongated telomere ends. Cse1 does not only support TLC1 import, but also the Sm-ring stabilization on the RNA enableling Mtr10 contact and nuclear import. Thus, Sm-ring formation and import factor contact resembles a quality control step in the maturation process of the telomerase. The re-imported immature TLC1 is finally trimmed into the 1158 nucleotides long mature form via the nuclear exosome. TMG-capping of TLC1 finalizes maturation, leading to mature telomerase.

scholarly journals Unraveling the stepwise maturation of the yeast telomerase

2021 ◽  
Author(s):  
Anna Greta Hirsch ◽  
Daniel Becker ◽  
Jan-Phillipp Lamping ◽  
Heike Krebber
Keyword(s):  
Nuclear Import ◽  
Model Organism ◽  
Reverse Transcriptase Activity ◽  
Type I ◽  
Short Telomere ◽  
Yeast Telomerase ◽  
Control Step ◽  
Import Receptors ◽  
Transport Factors ◽  
Cell Immortality

Telomerases elongate the ends of chromosomes required for cell immortality through their reverse transcriptase activity. By using the model organism Saccharomyces cerevisiae we defined the order in which the holoenzyme matures. First, a longer precursor of the telomerase RNA, TLC1 is transcribed and exported into the cytoplasm, where it associates with the protecting Sm-ring, the Est- and the Pop-proteins. This partly matured telomerase is re-import into the nucleus via Mtr10 and a novel TLC1-import factor, the karyopherin Cse1. Remarkably, while mutations in all known transport factors result in short telomere ends, mutation in CSE1 bypasses this defect and become Type I like survivors. Interestingly, both import receptors contact the Sm-ring for nuclear import, which therefore resembles a quality control step in the maturation process of the telomerase. The re-imported immature TLC1 is finally trimmed into the ~1150 nucleotide long mature form. TMG-capping of TLC1 finalizes maturation, leading to mature telomerase.

scholarly journals Nuclear Import of TFIIB Is Mediated by Kap114p, a Karyopherin with Multiple Cargo-binding Domains

2005 ◽  
Vol 16 (7) ◽  
pp. 3200-3210 ◽  
Author(s):  
Jennifer L. Hodges ◽  
Jennifer H. Leslie ◽  
Nima Mosammaparast ◽  
Yurong Guo ◽  
Jeffrey Shabanowitz ◽  
...  
Keyword(s):  
Nuclear Import ◽  
Binding Sites ◽  
Binding Domains ◽  
Transcription Factor Iib ◽  
General Transcription Factor ◽  
Proteomic Approach ◽  
Evolutionarily Conserved ◽  
Import And Export ◽  
Transport Factors

Nuclear import and export is mediated by an evolutionarily conserved family of soluble transport factors, the karyopherins (referred to as importins and exportins). The yeast karyopherin Kap114p has previously been shown to import histones H2A and H2B, Nap1p, and a component of the preinitiation complex (PIC), TBP. Using a proteomic approach, we have identified several potentially new cargoes for Kap114p. These cargoes include another PIC component, the general transcription factor IIB or Sua7p, which interacted directly with Kap114p. Consistent with its role as a Sua7p import factor, deletion of KAP114 led to specific mislocalization of Sua7p to the cytoplasm. An interaction between Sua7p and TBP was also detected in cytosol, raising the possibility that both Sua7p and TBP can be coimported by Kap114p. We have also shown that Kap114p possesses multiple overlapping binding sites for its partners, Sua7p, Nap1p, and H2A and H2B, as well as RanGTP and nucleoporins. In addition, we have assembled an in vitro complex containing Sua7p, Nap1p, and histones H2A and H2B, suggesting that this Kap may import several proteins simultaneously. The import of more than one cargo at a time would increase the efficiency of each import cycle and may allow the regulation of coimported cargoes.

scholarly journals Vectorial Import via a Metastable Disulfide-Linked Complex Allows for a Quality Control Step and Import by the Mitochondrial Disulfide Relay

Cell Reports ◽  
2019 ◽  
Vol 26 (3) ◽  
pp. 759-774.e5 ◽  
Author(s):  
Markus Habich ◽  
Silja Lucia Salscheider ◽  
Lena Maria Murschall ◽  
Michaela Nicole Hoehne ◽  
Manuel Fischer ◽  
...  
Keyword(s):  
Quality Control ◽  
Control Step ◽  
Quality Control Step

scholarly journals A Nuclear Import Pathway for a Protein Involved in tRNA Maturation

1997 ◽  
Vol 139 (7) ◽  
pp. 1655-1661 ◽  
Author(s):  
Jonathan S. Rosenblum ◽  
Lucy F. Pemberton ◽  
Günter Blobel
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Nuclear Import ◽  
Ribosomal Proteins ◽  
Ribosome Biogenesis ◽  
Sequence Similarity ◽  
Wild Type ◽  
Major Pathway ◽  
Trna Processing ◽  
Transport Factors ◽  
Limited Sequence

A limited number of transport factors, or karyopherins, ferry particular substrates between the cytoplasm and nucleoplasm. We identified the Saccharomyces cerevisiae gene YDR395w/SXM1 as a potential karyopherin on the basis of limited sequence similarity to known karyopherins. From yeast cytosol, we isolated Sxm1p in complex with several potential import substrates. These substrates included Lhp1p, the yeast homologue of the human autoantigen La that has recently been shown to facilitate maturation of pre-tRNA, and three distinct ribosomal proteins, Rpl16p, Rpl25p, and Rpl34p. Further, we demonstrate that Lhp1p is specifically imported by Sxm1p. In the absence of Sxm1p, Lhp1p was mislocalized to the cytoplasm. Sxm1p and Lhp1p represent the karyopherin and a cognate substrate of a unique nuclear import pathway, one that operates upstream of a major pathway of pre-tRNA maturation, which itself is upstream of tRNA export in wild-type cells. In addition, through its association with ribosomal proteins, Sxm1p may have a role in coordinating ribosome biogenesis with tRNA processing.

scholarly journals A Nucleus-based Quality Control Mechanism for Cytosolic Proteins

2010 ◽  
Vol 21 (13) ◽  
pp. 2117-2127 ◽  
Author(s):  
Rupali Prasad ◽  
Shinichi Kawaguchi ◽  
Davis T.W. Ng
Keyword(s):  
Quality Control ◽  
Control Systems ◽  
Ubiquitin Ligase ◽  
Nuclear Import ◽  
Control Mechanism ◽  
E3 Ubiquitin Ligase ◽  
26S Proteasome ◽  
Cytosolic Proteins ◽  
Hsp70 Chaperone ◽  
Quality Control Mechanism

Intracellular quality control systems monitor protein conformational states. Irreversibly misfolded proteins are cleared through specialized degradation pathways. Their importance is underscored by numerous pathologies caused by aberrant proteins. In the cytosol, where most proteins are synthesized, quality control remains poorly understood. Stress-inducible chaperones and the 26S proteasome are known mediators but how their activities are linked is unclear. To better understand these mechanisms, a panel of model misfolded substrates was analyzed in detail. Surprisingly, their degradation occurs not in the cytosol but in the nucleus. Degradation is dependent on the E3 ubiquitin ligase San1p, known previously to direct the turnover of damaged nuclear proteins. A second E3 enzyme, Ubr1p, augments this activity but is insufficient by itself. San1p and Ubr1p are not required for nuclear import of substrates. Instead, the Hsp70 chaperone system is needed for efficient import and degradation. These data reveal a new function of the nucleus as a compartment central to the quality control of cytosolic proteins.

scholarly journals Crowdsourced MRI quality metrics and expert quality annotations for training of humans and machines

2018 ◽  
Author(s):  
Oscar Esteban ◽  
Ross W Blair ◽  
Dylan M Nielson ◽  
Jan C Varada ◽  
Sean Marrett ◽  
...  
Keyword(s):  
Quality Control ◽  
Image Quality ◽  
Visual Assessment ◽  
Quality Metrics ◽  
Machine Learning Algorithms ◽  
Mr Images ◽  
Image Quality Metrics ◽  
Control Step ◽  
Automated Quality Control ◽  
Expert Ratings

AbstractThe neuroimaging community is steering towards increasingly large sample sizes, which are highly heterogeneous because they can only be acquired by multi-site consortia. The visual assessment of every imaging scan is a necessary quality control step, yet arduous and time-consuming. A sizeable body of evidence shows that images of low quality are a source of variability that may be comparable to the effect size under study. We present the MRIQC Web-API, an open crowdsourced database that collects image quality metrics extracted from MR images and corresponding manual assessments by experts. The database is rapidly growing, and currently contains over 100,000 records of image quality metrics of functional and anatomical MRIs of the human brain, and over 200 expert ratings. The resource is designed for researchers to share image quality metrics and annotations that can readily be reused in training human experts and machine learning algorithms. The ultimate goal of the database is to allow the development of fully automated quality control tools that outperform expert ratings in identifying subpar images.

scholarly journals Cytosolic Hsp70 and co-chaperones constitute a novel system for tRNA import into the nucleus

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Akira Takano ◽  
Takuya Kajita ◽  
Makoto Mochizuki ◽  
Toshiya Endo ◽  
Tohru Yoshihisa
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Quality Control ◽  
Nuclear Import ◽  
Nuclear Export ◽  
Substrate Recognition ◽  
Structural Features ◽  
Nuclear Accumulation ◽  
Nucleotide Binding Domain ◽  
Trna Import ◽  
Trna Binding

tRNAs are unique among various RNAs in that they shuttle between the nucleus and the cytoplasm, and their localization is regulated by nutrient conditions. Although nuclear export of tRNAs has been well documented, the import machinery is poorly understood. Here, we identified Ssa2p, a major cytoplasmic Hsp70 in Saccharomyces cerevisiae, as a tRNA-binding protein whose deletion compromises nuclear accumulation of tRNAs upon nutrient starvation. Ssa2p recognizes several structural features of tRNAs through its nucleotide-binding domain, but prefers loosely-folded tRNAs, suggesting that Ssa2p has a chaperone-like activity for RNAs. Ssa2p also binds Nup116, one of the yeast nucleoporins. Sis1p and Ydj1p, cytoplasmic co-chaperones for Ssa proteins, were also found to contribute to the tRNA import. These results unveil a novel function of the Ssa2p system as a tRNA carrier for nuclear import by a novel mode of substrate recognition. Such Ssa2p-mediated tRNA import likely contributes to quality control of cytosolic tRNAs.

The molecular mechanism of translocation through the nuclear pore complex is highly conserved

2002 ◽  
Vol 115 (14) ◽  
pp. 2997-3005
Author(s):  
Carl Feldherr ◽  
Debra Akin ◽  
Trevor Littlewood ◽  
Murray Stewart
Keyword(s):  
Nuclear Import ◽  
Amoeba Proteus ◽  
Nuclear Pore ◽  
Hnrnp A1 ◽  
Transport Mechanisms ◽  
Evolutionary Changes ◽  
Transport Receptors ◽  
Importin Α ◽  
Transport Factors

In this report we investigated the activity of vertebrate nuclear transport factors in a primitive organism, Amoeba proteus, to better understand evolutionary changes in the transport mechanisms of organisms expected to have different requirements for nucleocytoplasmic exchange. It was initially determined that FxFG-containing nucleoporins and Ran, both of which are essential for nuclear import in vertebrates, as well as yeast, are also present and functional in amoebae. This suggests that there are fundamental similarities in the transport process; however, there are also significant differences. Transport substrates containing either the hnRNP A1 M9 shuttling signal (a GST/GFP/M9 fusion protein) or the classical bipartite NLS (colloidal gold coated with BSA-bipartite NLS conjugates), both of which are effectively transported in vertebrate cells, are excluded from the nucleus when microinjected into amoebae. However, when these substrates are injected along with transportin or importin α/β, respectively, the vertebrate receptors for these signals, they readily accumulate in the nucleoplasm. These results indicate that although the molecular recognition of substrates is not well conserved between vertebrates and amoebae, vertebrate transport receptors are functional in A. proteus, showing that the translocation machinery is highly conserved. Since selected nuclear import pathways can be investigated in the absence of competing endogenous transport, A. proteus might provide a useful in vivo system for investigating specific molecular interactions involved in trafficking.

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