Gene expression of mtDNA- and nuclear-encoded genes coding for mitochondrial proteins. A. RNA gel blot analysis of mitochondrial genes. 10 μg of total RNA extracted from 100 mg of mature leaf tissue were separated on a 1.2% agarose gel and blotted onto a nylon membrane. PCR-amplified probes were used for the detection of the indicated genes. Ethidium bromide-stained 25S rRNA provides the RNA loading control. B. RT-PCR was performed on Col-0, KO and OEX total RNA extracted from leaves of 4 week old plants. Amplified genes are indicated. Semi-quantitative conditions and primers for β-tubulin amplification were used to ensure adequate loading for all samples.