Published online 9 December 2005
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The leucine rich region of DNA-PKcs contributes to its innate DNA affinity
Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine Michigan State University East Lansing, MI 48824, USA 1Department of Microbiology and Molecular Genetics, College of Veterinary Medicine Michigan State University East Lansing, MI 48824, USA
*To whom correspondence should be addressed. Tel: +1 517 432 9505; Fax: +1 517 353 9004; Email: kmeek{at}msu.edu
Received September 29, 2005. Revised November 14, 2005. Accepted November 14, 2005.
DNA-PK is a protein complex that consists of a DNA-binding, regulatory subunit [Ku] and a larger 
465 kDa catalytic subunit [DNA-PKcs], a serine/threonine protein kinase. The kinase activity of DNA-PKcs resides between residues 3745 and 4013, a PI3 kinase domain. Another recognized domain within this large protein is a leucine zipper (LZ) motif or perhaps more appropriately designated a leucine rich region (LRR) that spans residues 1503–1602. Whereas, DNA-PK's kinase activity has been shown to be absolutely indispensable for its function in non-homologous end joining (NHEJ), little is known about the functional relevance of the LRR. Here we show that DNA-PKcs with point mutations in the LRR can only partially reverse the radiosensitive phenotype and V(D)J recombination deficits of DNA-PKcs deficient cells. Disruption of the LRR motif affects the ability to purify DNA-PKcs via its binding to DNA-cellulose, but does not affect its interaction with Ku or its catalytic activity. These data suggest that the LRR region of DNA-PKcs may contribute to its intrinsic DNA affinity, and moreover, that intrinsic DNA binding is important for optimal function of DNA-PKcs in repairing double strand breaks in living cells.
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