Differential regulation of human mitochondrial promoters by transcription factor A

Oxidative phosphorylation in mitochondria requires proteins encoded by mitochondrial DNA. Therefore, misregulation of mitochondrial transcription will likely cause and/or exacerbate disease. The three mitochondrial promoters are believed to have the same transcription factor requirements for utilization. We have recently reconstituted human mitochondrial transcription in vitro by using recombinant proteins produced in a bacterial system and oligonucleotide‐based templates. With this system, we show that each promoter exhibits a unique dependence of transcription factor A (TFA). Particularly noteworthy is the observation that transcription initiation from the HSP2 promoter is independent of TFA and is, in fact, inhibited by TFA. Experiments designed to test models for inhibition of HSP2 transcription by TFA are consistent with TFA binding downstream of the transcription start site and preventing transcription elongation. Interestingly, inhibition of human HSP2 transcription is also observed by using mouse and bovine TFAs. Together, our studies provide the first evidence for differential regulation of the three human mitochondrial promoters and identify TFA as a key contributor to this regulation.