4.3. Mitochondrial transcriptional effects
Akin to bacterial DNA, mtDNA is an intronless, circular molecule of about 16.6 kb that lacks histones and it encodes 37 genes. Of the thousands of proteins in the mitochondrial proteome, mtDNA encodes 13 proteins are the essential component of the enzyme complexes of the oxidative phosphorylation system. In mammals, the mitochondrial genome is maternally inherited and unlike the nuclear genome in non-dividing, terminally differentiated cells, mtDNA is continuously replicated during mitochondrial reproduction [95]. The strands of the DNA duplex can be distinguished as heavy (H) and light (L) strand based upon the G + T base composition which results in different buoyant densities of each stand. Most information is encoded on the H strand, with genes for 2 rRNAs, 14 tRNAs, and 12 proteins. The L strand codes the other 8 tRNAs and a single protein. Many of the electron transport chain components encoded by mitochondrial genome are regulated by estrogens. Van Itallie and Dannies [96] found a 16-fold increase of cytochrome c oxidase subunit II mRNA upon 17β-E2 treatment in rat pituitary tumor cells.