Contact sites between inner and outer membranes

Contact sites between both mitochondrial membranes play a
predominant role in the transport of nuclear-coded precursor
proteins into mitochondria. The characterization of contact sites
was greatly advanced by the reversible accumulation of precursor
proteins in transit (translocation intermediates). It was found
that the sites are saturable, apparently contain proteinaceous
components and mediate extensive unfolding of the polypeptide chain
in translocation. Some components of mitochondrial contact sites
are currently being identified.