ABSTRACT
Overview Cells must ensure that each newly synthesized protein is sorted to its correct location where it can carry out the appropriate function. This process is called protein targeting. In a eukaryotic cell, the protein may be destined to stay in the cytosol, for example an enzyme involved in glycolysis (Section J3). Alternatively, it may need to be targeted to an organelle (such as a mitochondrion, lysosome, peroxisome, chloroplast or the nucleus) or be inserted into the plasma membrane or exported out of the cell (Section A2). In bacteria such as E. coli, the protein may stay in the cytosol, be inserted into the plasma membrane or the outer membrane, be sent to the space between these two membranes (the periplasmic space) or be exported from the cell (Section A1). In both prokaryotes and eukaryotes, if a protein is destined for the cytosol, it is made on ribosomes in the cytosol and released directly into the cytosol. If it is destined for other final locations, specific protein-targeting mechanisms are involved.
