A respiration-deficient Chinese hamster cell line with a defect in mitochondrial protein synthesis: Rapid turnover of some mitochondrial transcripts

Translational initiation and elongation in mammalian mitochondria is still poorly understood, and genetic approaches are expected to be helpful in the elucidation of the mechanism. This study describes a further characterization of a Chinese hamster mutant cell line which is severely defective in mitochondrial protein synthesis. Additional proof is provided that the mutation is nuclear. It is shown that there is no dramatic depletion of mitochondrial DNA in these cells, and the mtDNA appears to have neither significant deletions nor rearrangements. Transcription is not affected, and the polycistronic transcripts are processed normally. However, mt mRNAs are differentially quite unstable, and some are at very low steady state levels. Several nuclear transcripts encoding mitochondrial proteins were also investigated and found to be present at normal levels, and in particular, it was demonstrated that complex II (and succinate dehydrogenase activity), encoded entirely by nuclear genes, was only moderately affected by the absence of all the other complexes of the electron transport chain.