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Differences in the single-stranded DNA binding activities of MCM2-7 and MCM467: MCM2 and MCM5 define a slow ATP-dependent step.

The MCM2-7 complex, a hexamer containing six distinct and essential subunits, is postulated to be the eukaryotic replicative DNA helicase. Although all six subunits function at the replication fork, only a specific subcomplex consisting of the MCM4, 6, and 7 subunits (MCM467) and not the MCM2-7 complex exhibits DNA helicase activity in vitro. To understand why MCM2-7 lacks helicase activity and to address the possible function of the MCM2, 3, and 5 subunits, we have compared the biochemical properties of the Saccharomyces cerevisiae MCM2-7 and MCM467 complexes. We demonstrate that both complexes are toroidal and possess a similar ATP-dependent single-stranded DNA (ssDNA) binding activity, indicating that the lack of helicase activity by MCM2-7 is not due to ineffective ssDNA binding. We identify two important differences between them. MCM467 binds dsDNA better than MCM2-7. In addition, we find that the rate of MCM2-7/ssDNA association is slow compared with MCM467; the association rate can be dramatically increased either by preincubation with ATP or by inclusion of mutations that ablate the MCM2/5 active site. We propose that the DNA binding differences between MCM2-7 and MCM467 correspond to a conformational change at the MCM2/5 active site with putative regulatory significance.

Pubmed ID: 17895243

Authors

  • Bochman ML
  • Schwacha A

Journal

The Journal of biological chemistry

Publication Data

November 16, 2007

Associated Grants

None

Mesh Terms

  • Adenosine Triphosphate
  • Binding Sites
  • Binding, Competitive
  • Cell Cycle Proteins
  • Chromosomal Proteins, Non-Histone
  • DNA Helicases
  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • Dose-Response Relationship, Drug
  • Fungal Proteins
  • Kinetics
  • Minichromosome Maintenance Complex Component 4
  • Minichromosome Maintenance Complex Component 6
  • Models, Biological
  • Molecular Conformation
  • Nucleotides
  • Protein Binding
  • Protein Structure, Tertiary
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Time Factors