Control of mitochondrial transcription by thyroid hormone.

Thyroid hormone regulation of rat liver mitochondrial transcription was investigated. Steady-state levels of mitochondrial transcripts were measured by Northern blot analysis using cloned fragments of rat mtDNA. Thyroid hormone increased the steady-state concentrations of all mitochondrial mRNAs by 2-8 fold after 1-3 days of hormone treatment, whereas no significant change in the mitochondrial rRNA was observed. Analysis of transcript synthesis in isolated mitochondria shows that part or all of this increase is accounted for by elevated synthesis. Mechanisms by which thyroid hormone regulates transcription of the mitochondrial genome are discussed.