Twin-arginine translocation (Tat)-mediated protein trans-port across the bacterial cytoplasmicmembrane occurs only after synthesis and folding of the substrate protein that contains a signal peptide with a characteristic twin-arginine motif. This implies that premature contact between the Tat signal peptide and the Tat translocon in themembranemust be prevented. We used site-specific photo-crosslinking to demonstrate that the signal peptide of nascent Tat proteins is in close proximity to the chaperone and peptidyl-prolyl isomerase trigger factor (TF). .
