Cooperativity between the Ribosome-Associated Chaperone Ssb/RAC and the Ubiquitin Ligase Ltn1 in Ubiquitination of Nascent Polypeptides

The ribosome-associated chaperone Zuo1 controls translation upon TORC1 inhibition

Protein requirements of eukaryotic cells are ensured by proteostasis, which is mediated by tight control of TORC1 activity. Upon TORC1 inhibition, protein degradation is increased and protein synthesis is reduced through inhibition of translation initiation to maintain cell viability. Here, we show that the ribosome-associated complex (RAC)/Ssb chaperone system, composed of the HSP70 chaperone Ssb and its HSP40 co-chaperone Zuo1, is required to maintain proteostasis and cell viability under TORC1 inhibition in Saccharomyces cerevisiae. In the absence of Zuo1, translation does not decrease in response to the loss of TORC1 activity. A functional interaction between Zuo1 and Ssb is required for proper translational control and proteostasis maintenance upon TORC1 inhibition. Furthermore, we have shown that the rapid degradation of eIF4G following TORC1 inhibition is mediated by autophagy and is prevented in zuo1Δ cells, contributing to decreased survival in these conditions. We found that autophagy is defective in zuo1Δ cells, which impedes eIF4G degradation upon TORC1 inhibition. Our findings identify an essential role for RAC/Ssb in regulating translation in response to changes in TORC1 signalling.

Yeast Chaperone Hsp70-Ssb Modulates a Variety of Protein-Based Heritable Elements

Prions are transmissible self-perpetuating protein isoforms associated with diseases and heritable traits. Yeast prions and non-transmissible protein aggregates (mnemons) are frequently based on cross-β ordered fibrous aggregates (amyloids). The formation and propagation of yeast prions are controlled by chaperone machinery. Ribosome-associated chaperone Hsp70-Ssb is known (and confirmed here) to modulate formation and propagation of the prion form of the Sup35 protein [PSI⁺]. Our new data show that both formation and mitotic transmission of the stress-inducible prion form of the Lsb2 protein ([LSB⁺]) are also significantly increased in the absence of Ssb. Notably, heat stress leads to a massive accumulation of [LSB⁺] cells in the absence of Ssb, implicating Ssb as a major downregulator of the [LSB⁺]-dependent memory of stress. Moreover, the aggregated form of Gγ subunit Ste18, [STE⁺], behaving as a non-heritable mnemon in the wild-type strain, is generated more efficiently and becomes heritable in the absence of Ssb. Lack of Ssb also facilitates mitotic transmission, while lack of the Ssb cochaperone Hsp40-Zuo1 facilitates both spontaneous formation and mitotic transmission of the Ure2 prion, [URE3]. These results demonstrate that Ssb is a general modulator of cytosolic amyloid aggregation, whose effect is not restricted only to [PSI⁺].

Clinical Relevance of Secreted Small Noncoding RNAs in an Embryo Implantation Potential Prediction at Morula and Blastocyst Development Stages

Despite the improvements in biotechnological approaches and the selection of controlled ovarian hyperstimulation protocols, the resulting pregnancy rate from in vitro fertilization (IVF) protocols still does not exceed 30-40%. In this connection, there is an acute question of the development of a non-invasive, sensitive, and specific method for assessing the implantation potential of an embryo. A total of 110 subfertile couples were included in the study to undergo the IVF/ICSI program. Obtained embryos for transfer into the uterine cavity of patient cohort 1 (n = 60) and cohort 2 (n = 50) were excellent/good-quality blastocysts, and small noncoding RNA (sncRNA) content in the corresponding spent culture medium samples at the morula stage (n = 43) or at the blastocyst stage (n = 31) was analyzed by deep sequencing followed by qRT-PCR in real time. Two logistic regression models were developed to predict the implantation potential of the embryo with 100% sensitivity and 100% specificity: model 1 at the morula stage, using various combinations of hsa_piR_022258, hsa-let-7i-5p, hsa_piR_000765, hsa_piR_015249, hsa_piR_019122, and hsa_piR_008112, and model 2 at the blastocyst stage, using various combinations of hsa_piR_020497, hsa_piR_008113, hsa-miR-381-3p, hsa_piR_022258, and hsa-let-7a-5p. Protein products of sncRNA potential target genes participate in the selective turnover of proteins through the ubiquitination system and in the organization of the various cell cytoskeleton and nucleoskeleton structures, regulating the activity of the Hippo signaling pathway, which determines the fate specification of the blastomers.

Cell-free Translation: Preparation and Validation of Translation-competent Extracts from Saccharomyces cerevisiae

Cell-free translation is a powerful technique for in vitro protein synthesis. While cell-free translation platforms prepared from bacterial, plant, and mammalian cells are commercially available, yeast-based translation systems remain proprietary knowledge of individual labs. Here, we provide a detailed protocol for simple, fast, and cost-effective preparation of the translation-competent cell-free extract (CFE) from budding yeast. Our protocol streamlines steps combined from different procedures published over the last three decades and incorporates cryogenic lysis of yeast cells to produce a high yield of the translationally active material. We also describe techniques for the validation and troubleshooting of the quality and translational activity of the obtained yeast CFE. Graphic abstract: The flow of Cell-Free Extract (CFE) preparation procedure.