The transcription factors B1 (TFB1M, 607033) and B2 (TFB2M) are necessary for basal transcription of mammalian mitochondrial DNA. Human TFB1M and TFB2M are expressed ubiquitously and can each support promoter-specific mtDNA transcription in a pure recombinant in vitro system containing mitochondrial RNA polymerase and mitochondrial transcription factor A. TFB2M has been found to be at least 1 order of magnitude more active in promoting transcription than TFB1M. Both factors are highly homologous to bacterial rRNA dimethyltransferases, which suggests that an RNA-modifying enzyme has been recruited during evolution to function as a mitochondrial transcription factor.Synonyms: Dimethyladenosine transferase 2 mitochondrial, Hepatitis C virus NS5A-transactivated protein 5, Mitochondrial 12S rRNA dimethylase 2, Mitochondrial transcription factor B2, N'-adenosyl(rRNA) dimethyltransferase 2, NS5ATP5, S-adenosylmethionine-6-N', mtTFB2