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Mol. Cell. Biol., 09 1996, 5186-5193, Vol 16, No. 9
X Wu and MR Lieber
DNA ends are generated during double-strand-break repair and recombination.
A p70-p86 heterodimer, Ku, accounts for the DNA end binding activity in
eukaryotic cell extracts. When one or both subunits of Ku are missing,
mammalian cells are deficient in double-strand-break repair and in
specialized recombination, such as V(D)J recombination. Little is known of
which regions of Ku70 and Ku86 bind to each other to form the heterodimeric
complex or of which regions are important for DNA end binding. We have done
genetic and biochemical studies to examine the domains within the two
subunits important for protein assembly and for DNA end binding. We found
that the C-terminal 20-kDa region of Ku70 and the C-terminal 32-kDa region
of Ku86 are important for subunit-subunit interaction. For DNA binding,
full-length individual subunits are inactive, indicating that heterodimer
assembly precedes DNA binding. DNA end binding activity by the heterodimer
requires the C-terminal 40-kDa region of Ku70 and the C-terminal 45-kDa
region of Ku86. Leucine zipper-like motifs in both subunits that have been
suggested as the Ku70-Ku86 interaction domains do not appear to be the
sites of such interaction because these are dispensable for both assembly
and DNA end binding. On the basis of these studies, we have organized Ku70
into nine sequence regions conserved between Saccharomyces cerevisiae,
Drosophila melanogaster, mice, and humans; only the C-terminal three
regions are essential for assembly (amino acids [aa] 439 to 609), and the
C-terminal four regions appear to be essential for DNA end binding (aa 254
to 609). Within the minimal active fragment of Ku86 necessary for subunit
interaction (aa 449 to 732) and DNA binding (aa 334 to 732), a proline-rich
region is the only defined motif.
Copyright © 1996, American Society for Microbiology
Protein-protein and protein-DNA interaction regions within the DNA end- binding protein Ku70-Ku86
Division of Molecular Oncology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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