A conserved proline residue is present in the transmembrane-spanning domain of Tom7 and other tail-anchored protein subunits of the TOM translocase

The TOM translocase consists of several integral membrane proteins organised around the channel forming protein Tom40. Here we show that one of these protein subunits, Tom7, is a tail-anchored protein. The carboxy-terminal 33 amino acids of Tom7 contain the information for targeting the protein to the mitochondrial outer membrane, and a conserved proline residue within the transmembrane segment is required for efficient targeting of Tom7 to the outer membrane. An equivalent proline residue is important in targeting each of the other three tail-anchored proteins that associate with Tom40 to form the core of the TOM translocase.