PROTEIN-TRANSPORT ACROSS THE EUKARYOTIC ENDOPLASMIC-RETICULUM AND BACTERIAL INNER MEMBRANES

Protein transport across the endoplasmic reticulum membrane can occur by two pathways, a co- and a post-translational one. In both cases, po lypeptides are first targeted to translocation sites in the membrane b y virtue of their signal sequences and then transported across or inse rted into the phospholipid bilayer, most likely through a protein-cond ucting channel. Key components of the translocation apparatus have now been identified and the translocation pathways seem likely to be rela ted to each other but mechanistically distinct. Protein transport acro ss the bacterial inner membrane is both similar to and different from the process in eukaryotes. Other pathways of protein translocation exi st that bypass the ones involving classical signal sequences.