Termination within oligo(dT) tracts in template DNA by DNA polymerase gamma occurs with formation of a DNA triplex structure and is relieved by mitochondrial single-stranded DNA-binding protein

J Biol Chem. 1996 Nov 29;271(48):30774-80. doi: 10.1074/jbc.271.48.30774.


Xenopus laevis DNA polymerase gamma (pol gamma) exhibits low activity on a poly(dT)-oligo(dA) primer-template. We prepared a single-stranded phagemid template containing a dT41 sequence to test the ability of pol gamma to extend a primer through a defined oligo(dT) tract. pol gamma terminates in the center of this dT41 sequence. This replication arrest is abrogated by addition of single-stranded DNA-binding protein or by substitution of 7-deaza-dATP for dATP. These features are consistent with the formation of a T.A*T DNA triplex involving the primer stem. Replication arrest occurs under conditions that permit highly processive DNA synthesis by pol gamma. A similar replication arrest occurs for T7 DNA polymerase, which is also a highly processive DNA polymerase. These results suggest the possibility that DNA triplex formation can occur prior to dissociation of DNA polymerase. Primers with 3'-oligo(dA) termini annealed to a template with a longer oligo(dT) tract are not efficiently extended by pol gamma unless single-stranded DNA-binding protein is added. Thus, one of the functions of single-stranded DNA-binding protein in mtDNA maintenance may be to enable pol gamma to successfully replicate through dT-rich sequences.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Base Composition
  • DNA / metabolism*
  • DNA Polymerase III / metabolism*
  • DNA Replication*
  • DNA, Single-Stranded
  • DNA-Binding Proteins / metabolism*
  • Hydrogen-Ion Concentration
  • Nucleic Acid Conformation
  • Oligodeoxyribonucleotides / metabolism*
  • Templates, Genetic


  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • Oligodeoxyribonucleotides
  • oligo (dT)
  • oligodeoxyadenylic acid
  • DNA
  • DNA Polymerase III