Figure 6.

Effect of mtDNA depletion on transcription of mtDNA replication-associated genes. Three cell lines (143B, Δ16.10.40, and HP4) were subjected to a 15-d ethidium bromide treatment followed by an additional 15 d of growth in complete medium in the absence of ethidium bromide. Total RNA was obtained for all three cell lines at days 0, 15, and 30. These RNA samples as well as RNA from the 206 ρ° line were analyzed by Northern blots for five different transcripts (large subunit of the DNA polymerase γ, mitochondrial RNA polymerase, mitochondrial transcription factor A, mitochondrial single-strand–binding protein, and apocytochrome b). The graphs illustrate the variations in the ratio of the different RNAs to γ-actin (determined in the respective blots). There was no consistent up- or down-regulation of any of the nuclear-coded factors associated with the severe mtDNA depletion at day 15 or with the ρ° line (open squares). The graph for apocytochrome b was normalized to day 0, whereas the absolute ratios were plotted for the other RNAs. HP4 is a human xenomitochondrial cybrid harboring pigmy chimpanzee mtDNA.