The mitochondrial transcription and packaging factor Tfam imposes a U-turn on mitochondrial DNA

Nat Struct Mol Biol. 2011 Oct 30;18(11):1290-6. doi: 10.1038/nsmb.2159.


Tfam (transcription factor A, mitochondrial), a DNA-binding protein with tandem high-mobility group (HMG)-box domains, has a central role in the expression, maintenance and organization of the mitochondrial genome. It activates transcription from mitochondrial promoters and organizes the mitochondrial genome into nucleoids. Using X-ray crystallography, we show that human Tfam forces promoter DNA to undergo a U-turn, reversing the direction of the DNA helix. Each HMG-box domain wedges into the DNA minor groove to generate two kinks on one face of the DNA. On the opposite face, a positively charged α-helix serves as a platform to facilitate DNA bending. The structural principles underlying DNA bending converge with those of the unrelated HU family proteins, which have analogous architectural roles in organizing bacterial nucleoids. The functional importance of this extreme DNA bending is promoter specific and seems to be related to the orientation of Tfam on the promoters.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Base Sequence
  • Crystallography, X-Ray
  • DNA / chemistry
  • DNA / genetics
  • DNA / metabolism
  • DNA, Mitochondrial / chemistry*
  • DNA, Mitochondrial / metabolism
  • DNA-Binding Proteins / chemistry*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Genome, Mitochondrial
  • HMG-Box Domains / genetics
  • Humans
  • Mitochondrial Proteins / chemistry*
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Nucleic Acid Conformation*
  • Promoter Regions, Genetic
  • Protein Conformation*
  • Transcription Factors / chemistry*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*


  • DNA, Mitochondrial
  • DNA-Binding Proteins
  • Mitochondrial Proteins
  • TFAM protein, human
  • Transcription Factors
  • DNA

Associated data

  • PDB/3TMM