Precursor proteins in transit through mitochondrial contact sites interact with hsp70 in the matrix

We previously reported that hsp70 in the mitochondrial matrix
(mt-hsp70 = Ssc1p) is required for import of precursor proteins
destined for the matrix or intermembrane space. Here we show that
mt-hsp70 is also needed for the import of mitochondrial inner
membrane proteins. In particular, the precursor of ADP/ATP carrier
that is known not to interact with hsp60 on its assembly pathway
requires functional mt-hsp70 for import, suggesting a general role
of mt-hsp70 in membrane translocation of precursors. Moreover, a
precursor arrested in contact sites was specifically
co-precipitated with antibodies directed against mt-hsp70. We
conclude that mt-hsp70 is directly involved in the translocation of
many, if not all, precursor proteins that are transported across
the inner membrane.