SFP1-mediated prion-dependent lethality is caused by increased Sup35 aggregation and alleviated by Sis1.

[PSI+ ] is the prion form of the translation termination factor Sup35 (eRF3); [PSI+ ] strains display nonsense suppression. Another prion-like element, [ISP+ ], is linked to antisuppression in a specific background. Transcriptional regulator Sfp1 was shown to be responsible for [ISP+ ] propagation. In this work, we identified SFP1 as a multicopy inducer of [PSI+ ]-dependent lethality. Sfp1 is likely to up-regulate transcription of genes encoding release factors; however, its overproduction increases Sup35, but not Sup45 protein level. Using the synthetic lethality test, we compared the effects of SFP1 and SUP35 over-expression on the viability of [PSI+ ] strains. Together with an observation that Sfp1 overproduction leads to an increased accumulation of Sup35 in [PSI+ ] aggregates, we suggest that excess Sfp1 causes [PSI+ ] toxicity. Even though SUP45 over-expression is known to compensate for the [PSI+ ]-dependent lethality, it fails to do so when the lethality is caused by SFP1 over-expression. We discovered that the increased levels of Hsp40 chaperone Sis1 alleviate prion toxicity caused by either SFP1 or SUP35 over-expression and revert back to normal distribution of Sup35 between monomers and aggregate fractions. Finally, we showed that Sfp1 partially colocalizes with Sup35 aggregates, which may contribute to another mechanism of Sfp1-derived [PSI+ ] prion toxicity.

Temperature-induced reorganisation of Schistocephalus solidus (Cestoda) proteome during the transition to the warm-blooded host.

The protein composition of the cestode Schistocephalus solidus was measured in an experiment simulating the trophic transmission of the parasite from a cold-blooded to a warm-blooded host. The first hour of host colonisation was studied in a model experiment, in which sticklebacks Gasterosteus aculeatus infected with S. solidus were heated at 40°C for 1 h. As a result, a decrease in the content of one tegument protein was detected in the plerocercoids of S. solidus. Sexual maturation of the parasites was initiated in an experiment where S. solidus larvae were taken from fish and cultured in vitro at 40°C for 48 h. Temperature-independent changes in the parasite proteome were investigated by incubating plerocercoids at 22°C for 48 h in culture medium. Analysis of the proteome allowed us to distinguish the temperature-induced genes of S. solidus, as well as to specify the molecular markers of the plerocercoid and adult worms. The main conclusion of the study is that the key enzymes of long-term metabolic changes (glycogen consumption, protein production, etc.) in parasites during colonisation of a warm-blooded host are induced by temperature.

Chromosome-level genome assembly and structural variant analysis of two laboratory yeast strains from the Peterhof Genetic Collection lineage.

Thousands of yeast genomes have been sequenced with both traditional and long-read technologies, and multiple observations about modes of genome evolution for both wild and laboratory strains have been drawn from these sequences. In our study, we applied Oxford Nanopore and Illumina technologies to assemble complete genomes of two widely used members of a distinct laboratory yeast lineage, the Peterhof Genetic Collection (PGC), and investigate the structural features of these genomes including transposable element content, copy number alterations, and structural rearrangements. We identified numerous notable structural differences between genomes of PGC strains and the reference S288C strain. We discovered a substantial enrichment of mid-length insertions and deletions within repetitive coding sequences, such as in the SCH9 gene or the NUP100 gene, with possible impact of these variants on protein amyloidogenicity. High contiguity of the final assemblies allowed us to trace back the history of reciprocal unbalanced translocations between chromosomes I, VIII, IX, XI, and XVI of the PGC strains. We show that formation of hybrid alleles of the FLO genes during such chromosomal rearrangements is likely responsible for the lack of invasive growth of yeast strains. Taken together, our results highlight important features of laboratory yeast strain evolution using the power of long-read sequencing.

Estimation of amyloid aggregate sizes with semi-denaturing detergent agarose gel electrophoresis and its limitations.

Semi-denaturing detergent agarose gel electrophoresis (SDD-AGE) was proposed by Vitaly V. Kushnirov in the Michael D. Ter-Avanesyan's laboratory as a method to compare sizes of amyloid aggregates. Currently, this method is widely used for amyloid investigation, but mostly as a qualitative approach. In this work, we assessed the possibilities and limitations of the quantitative analysis of amyloid aggregate size distribution using SDD-AGE results. For this purpose, we used aggregates of two well-characterized yeast amyloid-forming proteins, Sup35 and Rnq1, and developed a protocol to standardize image analysis and process the result. A detailed investigation of factors that may affect the results of SDD-AGE revealed that both the cell lysis method and electrophoresis conditions can substantially affect the estimation of aggregate size. Despite this, quantitative analysis of SDD-AGE results is possible when one needs to estimate and compare the size of aggregates on the same gel, or even in different experiments, if the experimental conditions are tightly controlled and additional standards are used.

Whole genome sequencing data and analyses of the underlying SUP35 transcriptional regulation for a Saccharomyces cerevisiae nonsense suppressor mutant.

Termination of translation in eukaryotes is governed by two release factors encoded by the SUP45 and SUP35 genes in Saccharomyces cerevisiae. Previously, a set of mutations in these genes had been obtained. However, the exact sequence change associated with one mutation, sup35-222, was not identified by Sanger sequencing of the SUP35 region. Presented here are whole-genome sequencing data for the sup35-222 strain, data on copy number variation in its genome along with supporting pulse-field gel electrophoresis experiment data, and the list of single-nucleotide variations that differentiate this strain and its wild-type ancestor. One substitution upstream the SUP35 gene was located in a sequence corresponding to the Abf1-binding site. Data obtained from the introduction of this variation from sup35-222 strain into a different wild-type strain, specifically, detection of a nonsense-suppressor phenotype accompanied by a decrease in the Sup35 protein level, are also presented in this article.

Genome Sequencing and Comparative Analysis of Saccharomyces cerevisiae Strains of the Peterhof Genetic Collection.

The Peterhof genetic collection of Saccharomyces cerevisiae strains (PGC) is a large laboratory stock that has accumulated several thousands of strains for over than half a century. It originated independently of other common laboratory stocks from a distillery lineage (race XII). Several PGC strains have been extensively used in certain fields of yeast research but their genomes have not been thoroughly explored yet. Here we employed whole genome sequencing to characterize five selected PGC strains including one of the closest to the progenitor, 15V-P4, and several strains that have been used to study translation termination and prions in yeast (25-25-2V-P3982, 1B-D1606, 74-D694, and 6P-33G-D373). The genetic distance between the PGC progenitor and S288C is comparable to that between two geographically isolated populations. The PGC seems to be closer to two bakery strains than to S288C-related laboratory stocks or European wine strains. In genomes of the PGC strains, we found several loci which are absent from the S288C genome; 15V-P4 harbors a rare combination of the gene cluster characteristic for wine strains and the RTM1 cluster. We closely examined known and previously uncharacterized gene variants of particular strains and were able to establish the molecular basis for known phenotypes including phenylalanine auxotrophy, clumping behavior and galactose utilization. Finally, we made sequencing data and results of the analysis available for the yeast community. Our data widen the knowledge about genetic variation between Saccharomyces cerevisiae strains and can form the basis for planning future work in PGC-related strains and with PGC-derived alleles.