Project description:In protein synthesis, ribosome movement is not always smooth, rather often impeded by numerous reasons. Although the deceleration of ribosome defines the fates of the mRNAs and the synthesizing proteins, fundamental questions remain to be addressed including where ribosomes pause in mRNAs, what kind of RNA/amino acid context causes the pausing, and how physiologically significant the slowdown of protein synthesis is. Here we surveyed the position of ribosome collisions, caused by ribosome pausing, at a genome-wide level using the modified ribosome profiling in human and zebrafish. The collided ribosomes, i.e. disome, emerge at various sites; the proline-proline-lysine motif, stop codons, and 3′ UTR. The number of ribosomes in a collision is not limited to two, rather four to five, forming a queue of ribosomes. Especially, XBP1, a key modulator of unfolded protein response, shows striking queues of collided ribosomes thus acts as a substrate for ribosome-associated quality control (RQC) to avoid the accumulation of undesired proteins in the absence of stress. Our results provide an insight into the causes and the consequences of ribosome slowdowns by dissecting the specific architecture of ribosomes.
Project description:In protein synthesis, ribosome movement is not always smooth, rather often impeded by numerous reasons. Although the deceleration of ribosome defines the fates of the mRNAs and the synthesizing proteins, fundamental questions remain to be addressed including where ribosomes pause in mRNAs, what kind of RNA/amino acid context causes the pausing, and how physiologically significant the slowdown of protein synthesis is. Here we surveyed the position of ribosome collisions, caused by ribosome pausing, at a genome-wide level using the modified ribosome profiling in human and zebrafish. The collided ribosomes, i.e. disome, emerge at various sites; the proline-proline-lysine motif, stop codons, and 3′ UTR. The number of ribosomes in a collision is not limited to two, rather four to five, forming a queue of ribosomes. Especially, XBP1, a key modulator of unfolded protein response, shows striking queues of collided ribosomes thus acts as a substrate for ribosome-associated quality control (RQC) to avoid the accumulation of undesired proteins in the absence of stress. Our results provide an insight into the causes and the consequences of ribosome slowdowns by dissecting the specific architecture of ribosomes.
Project description:In protein synthesis, ribosome movement is not always smooth, rather often impeded by numerous reasons. Although the deceleration of ribosome defines the fates of the mRNAs and the synthesizing proteins, fundamental questions remain to be addressed including where ribosomes pause in mRNAs, what kind of RNA/amino acid context causes the pausing, and how physiologically significant the slowdown of protein synthesis is. Here we surveyed the position of ribosome collisions, caused by ribosome pausing, at a genome-wide level using the modified ribosome profiling in human and zebrafish. The collided ribosomes, i.e. disome, emerge at various sites; the proline-proline-lysine motif, stop codons, and 3′ UTR. The number of ribosomes in a collision is not limited to two, rather four to five, forming a queue of ribosomes. Especially, XBP1, a key modulator of unfolded protein response, shows striking queues of collided ribosomes thus acts as a substrate for ribosome-associated quality control (RQC) to avoid the accumulation of undesired proteins in the absence of stress. Our results provide an insight into the causes and the consequences of ribosome slowdowns by dissecting the specific architecture of ribosomes.
Project description:The ribosome collision due to translational stalling is recognized as a problematic event in translation by E3 ubiquitin ligase Hel2, leading to the non-canonical subunit dissociation followed by targeting of the faulty nascent peptides for degradation. Although Hel2-mediated quality control greatly contributes to maintaining cellular protein homeostasis, its physiological role in dealing with endogenous substrates remains unclear. Here we present a genome-wide analysis, based on selective ribosome profiling, to survey the endogenous substrates for Hel2. This reveals that Hel2 preferentially binds to the pre-engaged secretory ribosome-nascent-chain complexes (RNCs), which is translating upstream of targeting signals. Notably, Hel2 recruitment into secretory RNCs is elevated in the SRP-deficient condition; furthermore, the mitochondrial defects caused by insufficient SRP are enhanced by hel2 deletion, together with the mistargeting of secretory proteins into mitochondria. Collectively, our findings provide novel insights into the risk management in the secretory pathway for maintaining the cellular protein homeostasis.
Project description:The ribosome-associated protein quality control (RQC) system that resolves stalled translation events is activated when ribosomes collide and form disome, trisome or higher order complexes. However, it is unclear whether this system distinguishes collision complexes formed on defective mRNAs from those with functional roles on endogenous transcripts. Here, we performed disome and trisome footprint profiling in yeast and found collisions were enriched on diverse sequence motifs known to slow translation. When 60S recycling was inhibited, disomes accumulated at stop codons and could move into the 3’UTR to reinitiate translation. The ubiquitin ligase and RQC factor Hel2/ZNF598 generally recognized collisions but did not trigger degradation of endogenous transcripts. However, loss of Hel2 triggered the integrated stress response, via phosphorylation of eIF2alpha, thus linking these pathways. Our results suggest that Hel2 has a role in sensing ribosome collisions on endogenous mRNAs and such events may be important for cellular homeostasis.