Markedly Different ATP Requirements for RRNA Synthesis and MtDNA Light Strand Transcription Versus MRNA Synthesis in Isolated Human Mitochondria

In isolated mitochondria from HeLa cells, the ATP requirements for mitochondral DNA (mtDNA) transcription and RNA processing can be satisfied by either endogenous synthesis, mainly through oxidative-phosphorylation, or by exogenous supply. The pattern of RNA synthesis changes dramatically depending upon the level of ATP available. At the low intramitochondrial ATP levels produced from endogenous ADP in the presence of an oxidizable substrate and phosphate, the mRNA species are labeled to a substantial extent, whereas there is only a marginal labeling of the rRNA species and light (L) strand transcripts. By contrast, high ATP levels, either provided exogenously or produced endogenously in the presence of an oxidizable substrate, phosphate, and exogenous ADP, strongly stimulate rRNA synthesis (about 10-fold) and light (L) strand transcription (greater than 10-fold), with only a slight increase in mRNA synthesis.