7SL RNA and SRP orchestrate a global cellular response to acute thermal stress [RNA-seq]

Non-coding 7SL RNA is an ancestor to mammalian Alu and B1 SINE RNAs and is thought to function exclusively within the Signal Recognition Particle (SRP), aiding in the translocation of secretory proteins into the endoplasmic reticulum for export. Here, we discover a surprising new function unrelated to protein secretion. Under acute heat shock, 7SL and SRP together selectively arrest cellular transcription and translation machineries as a crucial early response to stress. Under thermal stress, 7SL is upregulated, localizes to the nucleus, and binds to target genes repressed by heat shock. Concurrently, in the cytosol, SRP binds to ribosomes and inhibits new protein synthesis. Translational suppression occurs independently of the signal peptide and is abrogated by depleting SRP. Intriguingly, translation inhibition extends to the mitochondria, as nuclear-encoded mitochondrial genes are enriched among SRP targets. Thus, apart from its role in protein export, 7SL/SRP orchestrates a global response to acute stress that encompasses the nucleus, cytosol, and mitochondria across transcription and translation.