(A) Model of the Sam50 β-barrel indicating loop 6 in peach and the conserved IRGF motif at the tip of loop 6 in red. The positions of residues 369 and 371 used for crosslinking in Fig. 7 are indicated. (B) Assembly of full-length β-barrel precursor proteins [35S]Por1, [35S]Mdm10 and [35S]Tom40 in wild-type (WT) and Sam50R366A mitochondria was analyzed by blue native electrophoresis and autoradiography. POR, Porin complex; SAM-Mdm10, SAM-Mdm10 complex; SAM-Ia, SAM-Ib and Int-II, assembly intermediates of Tom40. (C) Immobilized glutathione-S-transferase (GST)-fusion proteins carrying the Por1 β-signal were incubated with digitonin-lysed WT and Sam50R366A mitochondria. The β-signal was released by thrombin protease cleavage and eluates were analyzed by SDS-PAGE and immunodecoration. Load 12.5%; elution 100%.