Dynamic protein composition of Saccharomyces cerevisiae ribosomes in response to multiple stress conditions reflects alterations in translation activity.

Ribosomes, intercellular macromolecules responsible for translation in the cell, are composed of RNAs and proteins. While rRNA makes the scaffold of the ribosome and directs the catalytic steps of protein synthesis, ribosomal proteins play a role in the assembly of the subunits and are essential for the proper structure and function of the ribosome. To date researchers identified heterogeneous ribosomes in different developmental and growth stages. We hypothesized that under stress conditions the heterogeneity of the ribosomes may provide means to prepare the cells for quick recovery. Therefore the aim of the study was the identification of heterogeneity of ribosomal proteins within the ribosomes in response to eleven stress conditions in Saccharomyces cerevisiae, by means of a liquid chromatography/high resolution mass spectrometry (LC-HRMS) and translation activity tests. Out of the total of 74 distinct ribosomal proteins identified in the study 14 small ribosomal subunit (RPS) and 8 large ribosomal subunit (RPL) proteins displayed statistically significant differential abundances within the ribosomes under stress. Additionally, significant alterations in the ratios of 7 ribosomal paralog proteins were observed. Accordingly, the translational activity of yeast ribosomes was altered after UV exposure, during sugar starvation, cold shock, high salt, anaerobic conditions, and amino acid starvation.

Ribosome heterogeneity as a new element of translation regulation / Heterogenicznosc rybosomów jako nowy element regulacji translacji.

All living cells depend on the fine-tuning of gene expression and protein biosynthesis. Ribosomes, the molecular machines at the center of translation, have been previously considered the invariable driving force of protein production. However, recent studies indicated that the ribosomes are actively involved in the regulation of translation, influencing the control of translation initiation, the elongation speed, and the mRNA translation selectivity. This is due to the presence of subpopulations of the ribosomes, which differ in rRNAs and protein composition, their modifications and protein stoichiometry. In this publication, we focused our attention on the ribosomal heterogeneity in eukaryotes, which results from the changes in the stoichiometry of the ribosomal proteins and the existence of protein paralogs.

Levels of sdRNAs in cytoplasm and their association with ribosomes are dependent upon stress conditions but independent from snoRNA expression.

In recent years, a number of small RNA molecules derived from snoRNAs have been observed. Findings concerning the functions of snoRNA-derived small RNAs (sdRNAs) in cells are limited primarily to their involvement in microRNA pathways. However, similar molecules have been observed in Saccharomyces cerevisiae, which is an organism lacking miRNA machinery. Here we examined the subcellular localization of sdRNAs in yeast. Our findings reveal that both sdRNAs and their precursors, snoRNAs, are present in the cytoplasm at levels dependent upon stress conditions. Moreover, both sdRNAs and snoRNAs may interact with translating ribosomes in a stress-dependent manner. Likely consequential to their ribosome association and protein synthesis suppression features, yeast sdRNAs may exert inhibitory activity on translation. Observed levels of sdRNAs and snoRNAs in the cytoplasm and their apparent presence in the ribosomal fractions suggest independent regulation of these molecules by yet unknown factors.