A functional connection between translation elongation and protein folding at the ribosome exit tunnel in Saccharomyces cerevisiae

Proteostasis is a fundamental network of cellular pathways that ensures the optimal concentration and composition of correctly folded proteins within cells in normal and stress conditions. Among key components of this network are the molecular chaperones, which mediate protein folding but also act as modulators of protein synthesis. We have reported on a functional link between translation and de novo folding of proteins in the yeast Saccharomyces cerevisiae by uncovering a specific synthetic-lethal interaction between apparent unrelated mutant variants, the uL3[W255C] variant of the ribosomal protein uL3 and the null mutants of Zuo1 and Ssz1. Zuo1 and Ssz1 are components of the chaperone system named as ribosome-associated complex. Here, we performed a genome-wide analysis of ribosome dynamics by 5PSeq (Pelechano et al. 2015 PMID 2604644) in strains harbouring either wild-type uL3 or mutant uL3[W255C] in the presence or absence of Zuo1 or Ssz1. This method allows the study of ribosome dynamics, by sequencing 5’ phosphorylated mRNA co-translational degradation intermediates. Our results indicate that the rpl3[W255C] mutant is slightly impaired in translation elongation, defect that is significantly enhanced when combined with the deprivation of either Zuo1 or Ssz1.蛋白质稳态（Proteostasis）是一类核心的细胞通路网络，可在正常及应激条件下维持细胞内正确折叠蛋白质的最优浓度与组成。该网络的关键组分包括分子伴侣（molecular chaperones），其不仅介导蛋白质折叠过程，还可作为蛋白质合成的调控因子。我们此前曾在酿酒酵母（Saccharomyces cerevisiae）中报道了翻译与蛋白质从头折叠之间的功能关联：通过揭示两个看似无关的突变体变体间的特异性合成致死相互作用——核糖体蛋白uL3的uL3[W255C]突变体，以及Zuo1与Ssz1的基因敲除突变体。Zuo1与Ssz1属于名为核糖体相关复合物（ribosome-associated complex）的分子伴侣系统的组分。本研究中，我们通过5PSeq（Pelechano等，2015，PMID 2604644）对携带野生型uL3或突变型uL3[W255C]的菌株，在存在或缺失Zuo1或Ssz1的条件下开展了核糖体动态的全基因组分析。该方法通过测序共翻译降解的5’磷酸化mRNA中间产物，实现对核糖体动态的研究。我们的结果显示，rpl3[W255C]突变体的翻译延伸存在轻微缺陷，该缺陷在缺失Zuo1或Ssz1时会显著加剧。