Figure 6.

The requirement of mtHsp70 and Tim23 for the import of b₂-DHFR preproteins. (A) Requirement for mtHsp70. pb₂-DHFR, pb₂(▵47–65)-DHFR, and pb₂(QIC)-DHFR were imported into mitochondria isolated from the scc1–3 mutant strain and the corresponding wild-type strain (WT). The mitochondria were incubated at 37°C for 15 min before import (3% BSA in import buffer). After an import for 3 or 6 min at 25°C, all samples were treated with proteinase K (final concentration, 40 μg/ml) for 15 min on ice. After reisolation of the mitochondria, the proteins were separated by SDS-PAGE. (B) Requirement for Tim23. pb₂-DHFR, pb₂(▵47–65)-DHFR, and pb₂(QIC)-DHFR were imported into tim23–2 or the corresponding wild-type mitochondria for 5 min at 25°C. After import, the samples were treated as described above. For quantitation of the amount of protein imported into tim23–2 mitochondria, the import of the respective protein into wild-type mitochondria was set to 100% (control). Bars indicate the SEs of the means (from three to four independent experiments).