LAUSR

Significance Most of the proteins in all organisms are synthesized in the cell cytosol. However, a substantial fraction of these proteins have their function somewhere else, and cells therefore need protein targeting systems to relocate proteins during or after their synthesis. The signal recognition particle (SRP) is a universal player in protein targeting, but biochemical studies of its dynamics have been problematic since the geometric constraints inside living cells are hard to mimic in the test tube. Using single-molecule tracking, we have followed how SRP targets proteins to the membrane-bound translocation complexes, directly in living bacterial cells. Our kinetic measurements of the pathway will aid quantitative modeling and engineering of bacterial cells (e.g., for the production of medically relevant recombinant proteins).