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DNA-dependent protein kinase (Ku protein-p350 complex) assembles on double-stranded DNA

A Suwa1, M Hirakata, Y Takeda

  • 1Institute for Molecular Medicine and Genetics, Medical College of Georgia, Augusta 30912-3100.

Proceedings of the National Academy of Sciences of the United States of America
|July 19, 1994
PubMed

Insights

The Ku protein binds to DNA ends, forming a complex with p350. This interaction is crucial for assembling the DNA-dependent protein kinase (DNA-PK) holoenzyme, enabling DNA repair.

Area of Science:

  • Molecular Biology
  • Biochemistry
  • DNA Repair Mechanisms

Background:

  • The Ku protein, an autoantigen composed of 70- and 80-kDa polypeptides, is known to bind double-stranded DNA at free ends.
  • DNA-dependent protein kinase (DNA-PK) is a critical enzyme involved in DNA repair pathways.

Purpose of the Study:

  • To investigate the interaction of the Ku protein with other cellular components in the context of DNA binding.
  • To elucidate the role of Ku protein in the assembly of the DNA-PK holoenzyme.

Main Methods:

  • Immunoprecipitation of cellular structures from HeLa cell extracts using anti-Ku antibodies under varying salt concentrations.
  • Reconstitution experiments using purified Ku protein, p350 component, and double-stranded DNA.

Main Results:

  • Anti-Ku antibodies identified a complex of Ku protein and the 350-kDa component (p350) of DNA-PK associated with DNA under physiological conditions.
  • The Ku protein-p350 complex formation was dependent on the presence of double-stranded DNA in reconstitution assays.
  • The reconstituted complex exhibited catalytic activity, suggesting functional assembly.

Conclusions:

  • The Ku protein acts as a scaffold, interacting with DNA to facilitate the recruitment and binding of p350.
  • This interaction is a key step in the assembly of the catalytically active DNA-PK holoenzyme at DNA breaks.
  • Ku protein's role in DNA binding is essential for the formation of functional DNA-PK for DNA repair.

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