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Mol. Cell. Biol., 04 1996, 1519-1526, Vol 16, No. 4
A Errami, V Smider, WK Rathmell, DM He, EA Hendrickson, MZ Zdzienicka and G Chu
X-ray-sensitive hamster cells in complementation groups 4, 5, 6, and 7 are
impaired for both double-strand break repair and V(D)J recombination. Here
we show that in two mutant cell lines (XR-V15B and XR-V9B) from group 5,
the genetic defects are in the gene encoding the 86-kDa subunit of the Ku
autoantigen, a nuclear protein that binds to the double-stranded DNA ends.
These mutants express Ku86 mRNA containing deletions of 138 and 252 bp,
respectively, and the encoded proteins contain internal, in-frame deletions
of 46 and 84 amino acids. Two X-ray-resistant revertants of XR-V15B
expressed two Ku86 transcripts, one with and one without the deletion,
suggesting that reversion occurred by activation of a silent wild-type
allele. Transfection of full-length cDNA encoding hamster Ku86 into XR-V15B
cells resulted in a complete rescue of DNA-end-binding (DEB) activity and
Ku70 levels, suggesting that Ku86 stabilizes the Ku70 polypeptide. In
addition, cells expressing wild-type levels of DEB activity were fully
rescued for X-ray resistance and V(D)J recombination, whereas cells
expressing lower levels of DEB activity were only partially rescued. Thus,
Ku is an essential component of the pathway(s) utilized for the resolution
of DNA double-strand breaks induced by either X rays or V(D)J
recombination, and mutations in the Ku86 gene are responsible for the
phenotype of group 5 cells.
Copyright © 1996, American Society for Microbiology
Ku86 defines the genetic defect and restores X-ray resistance and V(D)J recombination to complementation group 5 hamster cell mutants
MGC-Department of Radiation Genetics and Chemical Mutagenesis, Leiden University, The Netherlands.
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