STOICHIOMETRY OF MITOCHONDRIAL TRANSCRIPTS AND REGULATION OF GENE-EXPRESSION BY MITOCHONDRIAL TRANSCRIPTION FACTOR-A

The steady state concentration of cytochrome c oxidase subunit I mRNA and 12 S rRNA, respectively, measured by a quantitative reverse transc ription/polymerase chain reaction method, was 4 and 15 molecules per m olecule of mt DNA in rat liver and 2 and 9 molecules in rat muscle, re spectively. These results imply that in the mitochondrial compartment, the molar concentration of all thirteen mRNAs by far exceeds the conc entration of ribosomes, a situation fundamentally different from the c ytosolic compartment. Following thyroid hormone treatment, both mitoch ondrial transcripts increased, in parallel with the mRNA encoding mito chondrial transcription factor A. We conclude that this transcription factor might be the rate limiting factor for mitochondrial transcripti on in vivo, at least under these conditions. (C) 1994 Academic Press, Inc.