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

The wheres and whys of protein translation Localized protein synthesis is important for a broad range of biological activities, from specifying the animal body plan to coordinating entry into the secretory pathway. Few tools are available that can investigate translation at specific subcellular sites. Jan et al. present a flexible ribosome profiling–based methodology to enable precise characterization of localized protein synthesis (see the Perspective by Shao and Hegde). Proximity-specific ribosome profiling provides a high-precision tool for looking at the mechanism of localized protein targeting and synthesis in living cells. The approach yielded a high-resolution systems-level view of cotranslational translocation at the endoplasmic reticulum. Williams et al. applied the technique to look at localized mRNA translation at the mitochondrial outer membrane. Science , this issue 10.1126/science.1257521 , p. 701 ; see also p. 748