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Human mitochondrial RNA polymerase structures reveal transcription start site and slippage mechanism

Jiayu Shen1, Quinten Goovaerts2, Yogeeshwar Ajjugal3

  • 1Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA; Graduate School of Biomedical Sciences at the Robert Wood Johnson Medical School of Rutgers University, Piscataway, NJ 08854, USA.

Molecular Cell
|July 25, 2025
PubMed

Insights

Researchers used cryo-EM to reveal how human mitochondrial transcription starts. They uncovered mechanisms for promoter melting, start site selection, and RNA slippage synthesis, providing key insights into mitochondrial DNA transcription regulation.

Area of Science:

  • Molecular Biology
  • Structural Biology
  • Genetics

Background:

  • Human mitochondrial DNA transcription is crucial for cellular energy production.
  • It is orchestrated by RNA polymerase (POLRMT) and initiation factors TFAM and TFB2M.
  • Understanding transcription initiation is key to deciphering mitochondrial gene expression regulation.

Purpose of the Study:

  • To elucidate the structural mechanisms of human mitochondrial transcription initiation.
  • To reveal how POLRMT, TFAM, and TFB2M cooperate during RNA synthesis.
  • To understand the pathways of normal and slippage transcription initiation.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) to determine high-resolution structures.
  • Biochemical assays to study transcription dynamics.
  • Structural analysis of transcription initiation intermediates.

Main Results:

  • Detailed structures of pre-catalytic, slipped-IC3, and slipped pre-IC4 intermediates were resolved.
  • Mechanisms for promoter melting, including specific base interactions, were identified.
  • The roles of TFB2M and POLRMT in guiding +1 start site selection and enabling -1 slippage synthesis were elucidated.

Conclusions:

  • The study reveals precise molecular mechanisms governing human mitochondrial transcription initiation.
  • Specific protein-DNA and protein-RNA interactions dictate start site selection and slippage.
  • Structural insights into apo and dimeric complexes suggest regulatory roles in transcription initiation.
Keywords:
POLRMTTFAMTFB2Mabortive synthesiscryo-EM structurelight strand promoterpromoter meltingslippage synthesisstart site selectiontranscription initiation

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