Translocon : don't pass me by

Translocon proteins are intimately involved with the proteins they import into the ER—including transmembrane portions of the incoming proteins, based on results from Peter McCormick, Arthur Johnson (Texas A&M University, College Station, TX), and colleagues.

Import of membrane proteins into the ER requires a joint effort between the 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 have very limited contacts with translocon proteins and are instead rapidly surrounded by phospholipids. But the new results show that the translocon is more than a passer-by in this process.

Johnson's group shows that imported transmembrane domains make...