Termination factor-mediated DNA loop between termination and initiation sites drives mitochondrial rRNA synthesis

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The human mitochondrial transcription termination factor (mTERF) is crucial for regulating heavy-strand rDNA transcription.
• mTERF's role in promoting transcription initiation, in addition to termination, was known, but the underlying mechanism remained unclear.

Purpose of the Study:

• To elucidate the mechanism by which mTERF stimulates mitochondrial rDNA transcription.
• To investigate the in vitro and in vivo roles of mTERF in rDNA transcription regulation.

Main Methods:

• Utilized a HeLa cell mitochondrial lysate-based reaction system with an artificial rDNA template.
• Performed in vitro transcription assays with and without mTERF.
• Investigated mTERF binding and rDNA loop formation in vivo.

Main Results:

• mTERF addition specifically stimulated rDNA transcription in vitro.
• Transcription stimulation required mTERF to bind simultaneously to both rDNA termination and initiation sites, forming a DNA loop.
• Evidence of mTERF-mediated double binding and rDNA loop formation was observed in vivo.

Conclusions:

• Human mitochondrial rRNA synthesis relies on mTERF-mediated rDNA looping to promote transcription machinery recycling.
• This looping mechanism facilitates the high rate of rDNA transcription required in human mitochondria.
• mTERF acts as a key regulator, orchestrating both initiation and termination through DNA looping.