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Author: Chernoff, Yury O. × End date: 2011 × Start date: 2011 × Type: Text ×

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Yeast model for studying heritable mammalian prion disease

2011-12-01 , Chernoff, Yury O.

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Identification of genes influencing synthetic lethality of genetic and epigenetic alterations in translation termination factors in yeast

2011 , Kiktev, D. A. , Chernoff, Yury O. , Archipenko, A. V. , Zhouravleva, G. A.

Translation termination in eukaryotic cells is determined by proteins Sup35 (eRF3) and Sup45 (eRF1) [1], which interact with a large number of partners [2]. In yeast Saccharomyces cerevisiae, protein Sup35 can form an aggregating epigenetically inherited conformer (prion) [PSI+] [3]. This prion is carried through the cytoplasm and causes disturbances in translation termination, which are phenotypically identified as the dominant omnipotent nonsense suppression. [PSI+] variants with different properties (nonsense suppression efficiency and transmission stability in mitosis) can be obtained in the same yeast strain. The presence of prion [PSI+] leads to lethality in the haploid yeast strain carrying mutations in the gene encoding another termination factor, Sup45 [4]. We have shown that the combination in the diploid strain of some mutant alleles of the SUP45 gene in the heterozygous state with prion [PSI+] entails the death of the hybrid [5]. The synthetic lethality of prion [PSI+] and mutant allele of the sup45 gene depends both on the type of mutant allele and the prion variant. Variant [PSI+], which is a strong suppressor (“strong” [PSI+], or [PSI+]S), causes synthetic lethality with all nonsense mutations and some missense mutations sup45 in the heterozygote. Our data indicate that the lethality of hybrids is correlated with a decreased activity of the Sup45 protein in the cell in case of sup45 mutations. This paper describes a test system that allows identification of proteins that affect the stability of prion [PSI+] and/or the efficiency of translation termination by their effect on the synthetic lethality of the prion conformer Sup35 and mutant alleles of SUP45. This test system is suitable to search for proteins that affect the translation termination efficiency and/ or prion maintenance in yeast cells. Gene library screening using this test system allowed us to identify the CUR1 gene, whose influence on another prion, [URE3], was shown earlier but the effect on translation termination factors was not known.

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Destabilization and recovery of a yeast prion after mild heat shock

2011-05-06 , Newnam, Gary P. , Birchmore, Jennifer L. , Chernoff, Yury O.

Yeast prion [PSI+] is a self-perpetuating amyloid of the translational termination factor Sup35. Although [PSI+] propagation is modulated by heat shock proteins (Hsps), high temperature was previously reported to have little or no effect on [PSI+]. Our results show that short-term exposure of exponentially growing yeast culture to mild heat shock, followed by immediate resumption of growth, leads to [PSI+] destabilization, sometimes persisting for several cell divisions after heat shock. Prion loss occurring in the first division after heat shock is preferentially detected in a daughter cell, indicating the impairment of prion segregation that results in asymmetric prion distribution between a mother cell and a bud. Longer heat shock or prolonged incubation in the absence of nutrients after heat shock lead to [PSI+] recovery. Both prion destabilization and recovery during heat shock depend on protein synthesis. Maximal prion destabilization coincides with maximal imbalance between Hsp104 and other Hsps such as Hsp70-Ssa. Deletions of individual SSA genes increase prion destabilization and/or counteract recovery. Dynamics of prion aggregation during destabilization and recovery is consistent with the notion that efficient prion fragmentation and segregation require a proper balance between Hsp104 and other (e. g. Hsp70- Ssa) chaperones. In contrast to heat shock, [PSI+] destabilization by osmotic stressors does not always depend on cell proliferation and/or protein synthesis, indicating that different stresses may impact the prion via different mechanisms. Our data demonstrate that heat stress causes asymmetric prion distribution in a cell division, and confirm that effects of Hsps on prions are physiologically relevant.

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Arra: genetic study of the yeast prion-interacting proteins

2011-02-28 , Chernoff, Yury O.

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