Structure of Escherichia coli exonuclease I suggests how processivity is achieved

Nat Struct Biol. 2000 Dec;7(12):1125-8. doi: 10.1038/81978.


Exonuclease I (ExoI) from Escherichia coli is a monomeric enzyme that processively degrades single stranded DNA in the 3' to 5' direction and has been implicated in DNA recombination and repair. Determination of the structure of ExoI to 2.4 A resolution using X-ray crystallography verifies the expected correspondence between a region of ExoI and the exonuclease (or proofreading) domains of the DNA polymerases. The overall fold of ExoI also includes two other regions, one of which extends the exonuclease domain and another that can be described as an elaborated SH3 domain. These three regions combine to form a molecule that is shaped like the letter C, although it also contains a segment that effectively converts the C into an O-like shape. The structure of ExoI thus provides additional support for the idea that DNA metabolizing enzymes achieve processivity by completely enclosing the DNA.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Binding Sites
  • Crystallography, X-Ray
  • DNA / chemistry
  • DNA / metabolism
  • DNA-Directed DNA Polymerase / chemistry
  • DNA-Directed DNA Polymerase / metabolism
  • Escherichia coli / enzymology*
  • Exodeoxyribonucleases / chemistry*
  • Exodeoxyribonucleases / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Structure, Tertiary
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Static Electricity
  • Structure-Activity Relationship
  • src Homology Domains


  • DNA
  • DNA-Directed DNA Polymerase
  • Exodeoxyribonucleases
  • exodeoxyribonuclease I

Associated data

  • PDB/1FXX