Comment on Principles of ER cotranslational translocation revealed by proximity-specific ribosome profiling

Jan et al. (Research Articles, 7 November 2014, p. 716) propose that ribosomes translating secretome messenger RNAs (mRNAs) traffic from the cytosol to the endoplasmic reticulum (ER) upon emergence of the signal peptide and return to the cytosol after termination. An accounting of controls demonstrates that mRNAs initiate translation on ER-bound ribosomes and that ribosomes are retained on the ER through many cycles of translation.