Reversal of the orientation of an integral protein of the mitochondrial outer membrane

The NH₂-terminus of the signal-anchor sequence of an integral, bitopic protein of the outer mitochondrial membrane was extended both in amino acid length (from 11 to 38 amino acids) and net charge (from +4 to +8)-changes that confer on the NH₂-terminus characteristics of a strong matrix-targeting signal. The protein was inserted into the outer membrane but in an inverted orientation (N_cyto-C_in). These findings suggest that, in common with other membrane systems, the orientation of a protein in the outer mitochondrial membrane can be determined by a signal that causes retention of the NH₂-terminus on the cytosolic side of the membrane.