title: Resistance of 3'-phosphoglycolate DNA ends to digestion by mammalian DNase III.
abstract: An essential step in the repair of free radical-mediated DNA strand breaks is the removal of sugar fragments such as phosphoglycolate from the 3' termini. While the abasic endonuclease Ape1 can remove phosphoglycolate from single-strand breaks in double-stranded DNA, an enzyme capable of removing it from 3' overhangs of double-strand breaks has yet to be identified. We therefore tested DNase III, the predominant 3' --> 5' exonuclease in mammalian cell extracts, for possible 3'-phosphoglycolate-removing activity. However, all 3'-phosphoglycolate substrates, as well as a 3'-phosphate substrate, were resistant to DNase III under conditions in which the analogous 3'-hydroxyl substrates were extensively degraded. The DNA end-binding protein Ku (an equimolar mixture of Ku70, now known as G22P1, and Ku86, now known as XRCC5) did not alter the resistance of the 3'-phosphoglycolate substrates, but the protein modulated the susceptibility of 3'-hydroxyl substrates, allowing DNase III to remove a 3' overhang but inhibiting digestion of the double-stranded portion of the substrate.
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
authors.forename: Kedar V
authors.initials: KV
authors.lastname: Inamdar
authors.forename: Yin
authors.initials: Y
authors.lastname: Yu
authors.forename: Lawrence F
authors.initials: LF
authors.lastname: Povirk
mesh_terms: D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000378:metabolism*; D005090:Exodeoxyribonucleases / Q000378:metabolism*; D006016:Glycolates / Q000378:metabolism*; D006868:Hydrolysis
chemical_list: D006016:Glycolates; D004247:DNA; D005090:Exodeoxyribonucleases; C020133:exodeoxyribonuclease III; C013193:phosphoglycolate