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. Introduction [PSI +], one of the best studied yeast prions, is formed by amyloid aggregates of the translation termination factor Sup35 (eRF3). Both translation termination factor genes SUP45 and SUP35 encoding eRF1 and eRF3, respectively, are essential in yeast Saccharomyces cerevisiae (see . The Sup35 protein consists of three domains. The Nproximal region (Sup35N), or prion-forming domain (PrD), is not essential for viability and translation termination (Ter-Avanesyan et al. 1993), but is required for [PSI + ] induction (Chernoff et al. 1992;Derkatch et al. 1996) and propagation (Ter-Avanesyan et al. 1994). The charged M (middle) region (Sup35M) is required for neither viability nor translation termination; however, it may influence [PSI + ] propagation. The C-proximal region (Sup35C) is required (and sufficient) for translation termination and cell viability; it also contains eRF1-interacting domain (see ], which is the prion form of the Rnq1 protein (Derkatch et al. 1997(Derkatch et al. , 2001).Malfunctioning of translation termination apparatus allows readthrough of stop codons leading to the suppression of nonsense mutations (see . It can be caused by a decrease in the level of functional Sup35 or Sup45 via different mechanisms. For example, the collection of sup45 and sup35 suppressor mutants includes viable nonsense mutants, in which the amount of eRF1 or ]-dependent toxicity during PIN4C over-expression (Yang et al. 2013(Yang et al. , 2014 ] cells. SFP1-fs induction in OT56 led to a statistically significant increase in both SUP35 and SUP45 mRNA levels (Fig. 1A). Quantitative RT-PCR showed a 1.51-and 1.50-fold increase in median mRNA levels of SUP35 and SUP45, respectively. We also confirmed an increase in SFP1 expression, because the median SFP1 mRNA level increased 2.96-fold (Fig. 1A).To determine whether SFP1 increases Sup35 and Sup45 production, we estimated the protein levels using Western blotting. How...

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.

Endemic amphipods (Amphipoda, Crustacea) of the most ancient and large freshwater Lake Baikal (Siberia, Russia) are a highly diverse group comprising >15% of all known species of continental amphipods. The extensive endemic biodiversity of Baikal amphipods provides the unique opportunity to study interactions and possible coevolution of this group and their parasites, such as Microsporidia. In this study, we investigated microsporidian diversity in the circulatory system of 22 endemic species of amphipods inhabiting littoral, sublittoral and deep-water zones in all three basins of Lake Baikal. Using molecular genetic techniques, we found microsporidian DNA in two littoral (Eulimnogammarus verrucosus, Eulimnogammarus cyaneus), two littoral/sublittoral (Pallasea cancellus, Eulimnogammarus marituji) and two sublittoral/deep-water (Acanthogammarus lappaceus longispinus, Acanthogammarus victorii maculosus) endemic species. Twenty sequences of the small subunit ribosomal (SSU) rDNA were obtained from the haemolymph of the six endemic amphipod species sampled from 0–60 m depths at the Southern Lake Baikal’s basin (only the Western shore) and at the Central Baikal. They form clusters with similarity to Enterocytospora, Cucumispora, Dictyocoela, and several unassigned Microsporidia sequences, respectively. Our sequence data show similarity to previously identified microsporidian DNA from inhabitants of both Lake Baikal and other water reservoirs. The results of our study suggest that the genetic diversity of Microsporidia in haemolymph of endemic amphipods from Lake Baikal does not correlate with host species, geographic location or depth factors but is homogeneously diverse.

Background Lake Baikal is one of the oldest freshwater lakes and has constituted a stable environment for millions of years, in stark contrast to small, transient bodies of water in its immediate vicinity. A highly diverse endemic endemic amphipod fauna is found in one, but not the other habitat. We ask here whether differences in stress response can explain the immiscibility barrier between Lake Baikal and non-Baikal faunas. To this end, we conducted exposure experiments to increased temperature and the toxic heavy metal cadmium as stressors. Results Here we obtained high-quality de novo transcriptome assemblies, covering mutiple conditions, of three amphipod species, and compared their transcriptomic stress responses. Two of these species, Eulimnogammarus verrucosus and E. cyaneus, are endemic to Lake Baikal, while the Holarctic Gammarus lacustris is a potential invader. Conclusions Both Baikal species possess intact stress response systems and respond to elevated temperature with relatively similar changes in their expression profiles. G. lacustris reacts less strongly to the same stressors, possibly because its transcriptome is already perturbed by acclimation conditions.