FIG. 1.

Mitochondrially encoded subunits assemble into intermediate subcomplexes. mtDNA-encoded subunits were pulse-chase labeled in wild-type lymphoblasts, followed by mitochondrial isolation. (A) Labeling profile of mtDNA-encoded subunits on SDS-PAGE. (B) BN-PAGE analysis of mitochondria solubilized in Triton X-100. mtDNA-encoded subunits were labeled without (left side) or following (right) CAP pretreatment. The letters a and b indicate regions of potential assembly intermediates. CI, complex I; CIII₂, complex III homodimer; CIV, complex IV; SC, CI/CIII₂ supercomplex. (C) Two-dimensional PAGE analysis of mitochondria isolated from radiolabeled lymphoblasts after 0, 1, 3, and 24 h of chase. For the first-dimension BN-PAGE, mitochondria were solubilized in 1% Triton X-100 as in panel B but at a higher mitochondrial protein/detergent ratio. Regions a and b include complex I intermediate subcomplexes containing subunits ND1, ND2, ND3, and ND6. Subunits CO1 (1), cytochrome b (2), CO3 (3), CO2 (4), ATP6 (5), and ATP8 (6) are indicated. CIV_i, complex IV intermediate.