Escorted by chaperones: Sti1 helps to usher precursor proteins from the ribosome to mitochondria

Little is known about factors that interact with mitochondrial precursor proteins in the cytosol. Employing site-specific crosslinking this study identifies chaperones of the Hsp70 and Hsp90 families as well as Sti1 as escorts of cytosolic preproteins. Sti1 presumably helps to hand-over preproteins from Hsp70 to the Hsp90 system and thereby facilitates their binding to TOM receptors on the mitochondrial surface.