The translocase of outer mitochondrial membrane (TOM) complex is a multisubunit complex involved in the recognition, unfolding, and translocation of preproteins into the mitochondria. TOM70, an important member of the TOM complex, contains a tetratricopeptide repeat domain similar to those found in cytosolic chaperones such as Hsp90 and Hsc70 and provides a docking site for these proteins. This interaction is thought to be a critical first step in the TOM70-dependent mitochondrial import, followed by contact between the preprotein and TOM70. After targeting to TOM70, preproteins are translocated through the outer membrane via the TOM40 import pore complex. The precise mechanism of how preproteins progress from TOM70 to TOM40 to full translocation is still unclear. At least two isoforms of TOM70 are known to exist.