Biology subjects

Collart, M.

Publications and source records attributed to Collart, M..

4 recordsLinked to original sources

bioRxiv2026

Puf3 contributes to changes in mRNA solubility, translation elongation dynamics at rare arginine codons and loss of protein homeostasis in cells lacking Not4

The Not proteins of the Ccr4-Not complex regulate translation elongation dynamics, essential for proper folding and assembly of new proteins. In yeast, ribosomes with non-optimal codons in the A-site are enriched within the pool of ribosomes bound by Not4 and Not5. Such ribosomes accumulate in cells lacking Not4 or Not5 that show defects in co-translational assembly and aggregation of new proteins. Recently we observed that depletion of Not1 and Not4 inversely regulate changes in mRNA solubility, correlating with inverse codon-specific changes in A-site ribosome dwelling occupancies (RDOs). Here we describe that mRNAs less soluble upon Not4 depletion are enriched for targets of the RNA-binding protein Puf3. We determine that Puf3 contributes to inverse changes of A-site RDOs upon Not1 and Not4 depletion, in particular at rare arginine codons, and it contributes to changes in mRNA solubility in not4{Delta}. Moreover, deletion of Puf3 suppresses temperature sensitivity and protein aggregation in the not4{Delta} strain, while overexpression of Puf3 is toxic. Puf3 post-translational modifications and the Puf3 interactome are altered in not4{Delta}. Taken together, our results associate alterations in Puf3 post-translational status and function, including contribution to translation elongation dynamics, with not4{Delta} mutant phenotypes. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/695943v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@855afdorg.highwire.dtl.DTLVardef@118addaorg.highwire.dtl.DTLVardef@13dd015org.highwire.dtl.DTLVardef@12824c6_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2022

Phase separated ribosome nascent chain complexes paused in translation are capable to continue expression of proteins playing role in genotoxic stress response upon DNA damage

EDTA- and RNase-resistant ribonucleoprotein complexes of arrested ribosomes with protruding nascent polypeptide chains have recently been described in yeast and human cells. These complexes have been termed assemblysomes, a type of soluble condensates distinct from other known granules. Here, we use bioinformatics to identify additional proteins that likely form assemblysomes during translation. We characterize soluble condensates of the DNA helicase Sgs1, one such identified protein and a key player in the repair of DNA double-strand breaks in yeast. We show that paused ribosome-associated nascent chains of Sgs1 in condensates are able to resume translation upon UV irradiation, consistent with the return of mRNA to the ribosome pool. By extending our studies to human cell lines, we found that EDTA-resistant pellets of ribosomes from the human prostate cancer cell line DU145 are sensitive to treatment with 1,6-hexanediol, which is known to dissolve liquid-liquid phase-separated condensates. In addition, transmission electron microscopy shows that 1,6-hexanediol dissolves ring ribosomal structures from the cytoplasm of radioresistant A549 cells while making the cells more sensitive to X-rays. These results suggest that the stress response is based on a conserved mechanism involving the regulated return of phase-separated paused ribosome-nascent chain complexes to translating ribosomes.

molecular biology↗

bioRxiv2022

Translational reprogramming in response to accumulating stressors ensures critical threshold levels of Hsp90 for mammalian life

The cytosolic molecular chaperone Hsp90 is essential for eukaryotic life1, 2. It is involved in multiple branches of proteostasis2, 3, and as a molecular capacitor in morphological evolution4. Although reduced Hsp90 levels cause phenotypic variations5, 6 and correlate with aging7, whether eukaryotic cells and organisms can tune the basal Hsp90 protein levels to alleviate physiologically accumulated stress is unknown. To begin to explore this question, we investigated whether and how mice adapt to the deletion of three out of four alleles encoding cytosolic Hsp90, one Hsp90{beta} allele being the only remaining one. While the vast majority of such mouse embryos die during gestation, survivors apparently manage to increase their Hsp90{beta} protein to at least wild-type levels. Further mechanistic studies revealed an internal ribosome entry site in the 5UTR of the Hsp90{beta} mRNA allowing translational reprogramming to compensate for the genetic loss of Hsp90 alleles and in response to stress. We found that the minimum amount of total Hsp90 that is required to support viability of mammalian cells and organisms is 50-70% of what is normally there. Those that fail to maintain a threshold level are subject to accelerated senescence, proteostatic collapse, and ultimately death. Therefore, considering that Hsp90 levels can be reduced [≥]100-fold in the unicellular budding yeast, critical threshold levels of Hsp90 have been markedly increased during eukaryotic evolution. The incompressible part of the steady-state levels of Hsp90 may have increased to accommodate the ever-growing complexity of the proteome8 on the path towards mammals.

molecular biology↗

bioRxiv2019

Switch from translation initiation to elongation needs Not4 and Not5 collaboration

Not4 and Not5 are crucial components of the Ccr4-Not complex with pivotal functions in mRNA metabolism. Both associate with ribosomes but mechanistic insights on their function remain elusive. Here we determine that Not5 and Not4 synchronously impact translation initiation and Not5 alone alters translation elongation. Deletion of Not5 causes elongation defects in a codon-dependent fashion, increasing and decreasing the ribosome dwelling occupancy at minor and major codons, respectively. This larger difference in codons translation velocities alters translation globally and enables kinetically unfavorable processes such as nascent chain deubiquitination to take place. In turn, this leads to abortive translation and favors protein aggregation. These findings highlight the global impact of Not4 and Not5 in controlling the speed of mRNA translation and transition from initiation to elongation. SummaryNot4 and Not5 regulate translation synchronously but distinguishably, facilitating smooth transition from initiation to elongation

molecular biology↗