ABSENCE OF A KU-LIKE DNA END BINDING-ACTIVITY IN THE XRS DOUBLE-STRAND DNA REPAIR-DEFICIENT MUTANT

Double-strand DNA break repair is important in maintaining the genetic integrity of the genome. Using a mobility shift assay, we find that a protein, or complex of proteins, that is present in mammalian and yea st cells binds to the ends of double-strand DNA and renders the ends r esistant to exonuclease digestion. Additionally, a mammalian DNA doubl e-strand repair-deficient mutant, xrs, has no observable DNA end bindi ng activity, while a revertant cell has wild-type activity. In additio n, mobility supershift assays using monoclonal antibodies to the human Ku antigen (M(r) 70,000 subunit) reveal that one of the proteins of t his end binding activity may be the Ku antigen or a protein with simil ar antigenic determinants. These observations suggest that this DNA en d-binding protein may function in DNA repair.