a, Cellular fractionation of wild-type, tom70∆ and mim1∆ cells. The data are representative for two (tom70∆) or three (mim1∆) independent experiments. b, Ubx2 levels in microsomal fraction of the indicated yeast strains. The data are representative of two independent experiments. c, [35S]Ubx2 was imported into wild-type and tom22∆ mitochondria and analysed by BN–PAGE and autoradiography. The data are representative of four independent experiments. d, Import of the indicated [35S]Ubx2 constructs into wild-type mitochondria on BN–PAGE. The data are representative of five independent experiments. TMD, transmembrane domain. Quantification of the Ubx2–TOM assembly. The assembly of Ubx2 wild type was set to 100% (control). Mean ± s.e.m. (n = 5).