Poly-adenosine diphosphate (ADP)-ribosylation of nuclear proteins has been demonstrated previously to be activated in vivo by the presence of DNA single-strand breaks and has thus been implicated to play an important role in altering chromatin structure during cellular recovery from DNA damage. Based upon these considerations, a novel immunofractionation method, using antipoly(ADP-ribose) coupled to Sepharose, has been used to enrich for those limited domains of chromatin undergoing

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... osylation. We have used three independent methods to verify the presence of significant levels of single-strand DNA breaks adjacent to polynucleosomes engaged in ADP-ribosylation.