TFB1M is a member of the methyltransferase superfamily. TFB1M is a dimethyltransferase which methylates mitochondrial 12S rRNA at the conserved stem loop. The TFB1M protein also is part of the basal mitochondrial transcription complex and is required for mitochondrial gene expression. TFB1M stimulates transcription independently of the methyltransferase activity.