The protein import machinery of the mitochondrial membranes.

Mitochondria are surrounded by two membranes that contain independent and non-related protein transport machineries. Remarkable progress was recently achieved in elucidating the structure of the outer membrane import channel and in the identification of new components involved in protein traffic across the intermembrane space and the inner membrane. Traditional concepts of protein targeting and sorting had to be revised. Here we briefly summarize the data on the mitochondrial protein import system with particular emphasis on new developments and perspectives.