Translocon

ribosome and the translocon to ensure that each domain of the translocating protein is targeted correctly to either the lumenal or cytoplasmic face of the ER. Transmembrane domains present an additional problem—the hydrophobic portion must move laterally past the translocon into the lipid bilayer. Current models suggest that membrane-spanning domains Transmembrane domains make prolonged contacts with the translocon. Jo hn so n/ El se vi er ometimes a step back is needed before going forward. Merridee Wouters, Ke Liu, Peter Riek, and Ahsan Husain (Victor Chang Cardiac Research Institute, Sydney, Australia) find that uniquely specialized serine proteases evolved in two steps: an ancestor protease first became more promiscuous and despecialized before its duplicated progeny were then respecialized. Serine proteases found in vertebrates today come in various flavors: trypsin-like enzymes cleave after basic residues, but nontrypsin-like proteases favor S