A specific loop in human DNA polymerase mu allows switching between creative and DNA-instructed synthesis

Nucleic Acids Res. 2006;34(16):4572-82. doi: 10.1093/nar/gkl457. Epub 2006 Sep 8.

Abstract

Human DNA polymerase mu (Polmu) is a family X member that has terminal transferase activity but, in spite of a non-orthodox selection of the template information, displays its maximal catalytic efficiency in DNA-templated reactions. As terminal deoxynucleotidyl transferase (TdT), Polmu has a specific loop (loop1) that could provide this enzyme with its terminal transferase activity. When loop1 was deleted, human Polmu lacked TdT activity but improved DNA-binding and DNA template-dependent polymerization. Interestingly, when loop1 from TdT was inserted in Polmu (substituting its cognate loop1), the resulting chimaera displayed TdT activity, preferentially inserting dGTP residues, but had a strongly reduced template-dependent polymerization activity. Therefore, a specialized loop in Polmu, that could adopt alternative conformations, appears to provide this enzyme with a dual capacity: (i) template independency to create new DNA information, in which loop1 would have an active role by acting as a 'pseudotemplate'; (ii) template-dependent polymerization, in which loop1 must allow binding of the template strand. Recent in vivo and in vitro data suggest that such a dual capacity could be advantageous to resolve microhomology-mediated end-joining reactions.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Catalysis
  • DNA / biosynthesis*
  • DNA / metabolism
  • DNA Nucleotidylexotransferase / chemistry
  • DNA, Single-Stranded / metabolism
  • DNA-Directed DNA Polymerase / chemistry*
  • DNA-Directed DNA Polymerase / genetics
  • DNA-Directed DNA Polymerase / metabolism
  • Humans
  • Molecular Sequence Data
  • Protein Binding
  • Protein Structure, Tertiary
  • Sequence Deletion
  • Templates, Genetic

Substances

  • DNA, Single-Stranded
  • DNA
  • DNA polymerase mu
  • DNA Nucleotidylexotransferase
  • DNA-Directed DNA Polymerase