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Defining the physiological role of SRP in protein-targeting efficiency and specificity

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Science  18 Jan 2018:
eaar3607
DOI: 10.1126/science.aar3607

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Abstract

The signal recognition particle (SRP) enables cotranslational delivery of proteins for translocation into the endoplasmic reticulum (ER), but its full in vivo role remains incompletely explored. We combined rapid auxin-induced SRP degradation with proximity-specific ribosome profiling to define SRP’s in vivo function in yeast. Despite the classic view that SRP recognizes N-terminal signal sequences, we show that SRP was generally essential for targeting transmembrane domains regardless of their position relative to the N terminus. By contrast, many proteins containing cleavable N-terminal signal peptides were efficiently cotranslationally targeted in SRP’s absence. We also revealed an unanticipated consequence of SRP loss: Normally ER-targeted transcripts were mistargeted to mitochondria, leading to mitochondrial defects. These results elucidate SRP’s essential roles in maintaining the efficiency and specificity of protein targeting.

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