Search

Consistent with its location on the ribosome, reporter assays demonstrate a role for Rps26 in recognition of the Kozak sequence. Consequently, Rps26-deficient ribosomes display preference for mRNAs encoding components of the high salt and high pH stress response pathways and accumulate in yeast exposed to high salt or pH. Here we use this information to reprogram the cellular response to high salt by introducing point mutations in the Kozak sequence of key regulators for the cell wall MAP-kinase, filamentation, or DNA repair pathways. This stimulates their translation upon genetic, or salt-induced Rps26 depletion from ribosomes. Stress resistance assays show activation of the targeted pathways in an Rps26- and salt-dependent manner. Genomic alterations in diverse yeast populations indicate that analogous tuning occurs during adaptation to ecological niches. Thus, evolution shapes translational control across the genome by taking advantage of the accumulation of diverse ribosome populations., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

We describe a novel approach to separate two ribosome populations from the same cells and use this method in combination with RNA-seq to identify mRNAs bound to Saccharomyces cerevisiae ribosomes with and without Rps26, a protein linked to the pathogenesis of Diamond-Blackfan anemia (DBA). These analyses reveal that Rps26 contributes to mRNA-specific translation by recognition of the Kozak sequence in well-translated mRNAs and that Rps26-deficient ribosomes preferentially translate mRNA from select stress-response pathways. Surprisingly, exposure of yeast to these stresses leads to the formation of Rps26-deficient ribosomes and to the increased translation of their target mRNAs. These results describe a novel paradigm: the production of specialized ribosomes, which play physiological roles in augmenting the well-characterized transcriptional stress response with a heretofore unknown translational response, thereby creating a feed-forward loop in gene expression. Moreover, the simultaneous gain-of-function and loss-of-function phenotypes from Rps26-deficient ribosomes can explain the pathogenesis of DBA.