Editing Mitochondrial DNA (section)

===Regulation of transcription===

The promoters for the initiation of the transcription of the heavy and light strands are located in the main non-coding region of the mtDNA called the displacement loop, the [[D-loop]].<ref name="pmid29945721" /> There is evidence that the transcription of the mitochondrial rRNAs is regulated by the heavy-strand promoter 1 (HSP1), and the transcription of the polycistronic transcripts coding for the protein subunits are regulated by HSP2.<ref name="pmid29945721" />

Measurement of the levels of the mtDNA-encoded RNAs in bovine tissues has shown that there are major differences in the expression of the mitochondrial RNAs relative to total tissue RNA.<ref name="1993-Raikhinstein">{{Cite journal |vauthors=Raikhinstein M, Hanukoglu I |date=November 1993 |title=Mitochondrial-genome-encoded RNAs: differential regulation by corticotropin in bovine adrenocortical cells |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=90 |issue=22 |pages=10509–10513 |bibcode=1993PNAS...9010509R |doi=10.1073/pnas.90.22.10509 |pmc=47806 |pmid=7504267 |doi-access=free}}</ref> Among the 12 tissues examined the highest level of expression was observed in the heart, followed by brain and steroidogenic tissue samples.<ref name="1993-Raikhinstein" />

As demonstrated by the effect of the trophic hormone [[ACTH]] on adrenal cortex cells, the expression of the mitochondrial genes may be strongly regulated by external factors, apparently to enhance the synthesis of mitochondrial proteins necessary for energy production.<ref name="1993-Raikhinstein" /> Interestingly, while the expression of protein-encoding genes was stimulated by ACTH, the levels of the mitochondrial 16S rRNA showed no significant change.<ref name="1993-Raikhinstein" />