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Characterization of an RNA polymerase activity from HeLa cell mitochondria, which initiates transcription at the heavy strand rRNA promoter and the light strand promoter in human mitochondrial DNA.

An RNA polymerase activity capable of initiating transcription at both the heavy strand rRNA promoter and the light strand promoter of human mitochondrial DNA has been partially purified from HeLa cell mitochondria and characterized in its requirements and products. The ratio of the two transcription initiating activities varied considerably from preparation to preparation. The human mtRNA polymerase partially purified by DEAE-cellulose and heparin-agarose chromatography exhibits a great sensitivity to ionic strength and to Mn2+, characteristics which clearly differentiate this enzyme from bacterial and eukaryotic nuclear RNA polymerases, and in contrast resemble the behavior of the yeast mtRNA polymerase. The human mtRNA polymerase exhibits a requirement for ATP which is 15- to 20-fold higher than that for the other NTPs, a low optimum template DNA concentration, and a marked susceptibility to inhibition by non-mitochondrial DNA.