Increased levels of mitochondrial gene expression in rat fibroblast cells immortalized or transformed by viral and cellular oncogenes.

Steady‐state levels of the mitochondrial (mt) mRNA encoding subunit II of cytochrome oxidase (COII) were increased 5‐10 fold in fully transformed cell lines derived from rodent embryonic fibroblasts after transfer of polyoma virus DNA, and in immortalized cell lines established by transfer of plt (polyoma large T protein), E1A (adenovirus) and myc oncogenes. Increased mitochondrial gene expression was not related with active growth per se: it was low in fast‐growing rat embryo cells, and it did not change upon serum starvation and subsequent stimulation of FR3T3 cells. The number of copies of mtDNA did not vary, and different mitochondrial mRNAs and rRNAs were increased in the same proportions, suggesting a change in the rate of accumulation of their common precursor.