Heat shock induces silent ribosomes and reorganizes mRNA turnover

mRNAs associate with single or multiple ribosomes; these ribosomal assemblies-monosomes and polysomes-translate the mRNAs before degradation. The impact of heat stress on this mRNA turnover remains unclear. We show that in heat-shocked yeast cells, the proportion of monosomes increases without a corresponding rise in the number of associated mRNAs. Consequently, most monosomes are devoid of mRNAs and silent, lacking translational initiation factors and proteins facilitating posttranslational folding. Such silent monosomes also appear under other stress conditions, with proportions varying according to stress type, suggesting that they represent a general feature of cellular adaptation. In parallel with the induction of silent ribosomes, elevated temperatures reduce the overall rate of mRNA-ribosome association with few exceptions. Notably, heat shock promotes the ribosomal association of transcripts encoding heat shock proteins, without extension of the half-lives of these mRNAs. These mechanisms dynamically reorganize mRNA turnover to prioritize the translation of heat shock proteins over other proteins.