CATALYTIC ACTIVITY OF POLY(ADP-RIBOSE) POLYMERASE IS NECESSARY FOR REPAIR OF N-METHYLPURINES IN NONTRANSCRIBED, BUT NOT IN TRANSCRIBED, NUCLEAR-DNA SEQUENCES

The role of poly(ADP-ribose) polymerase (PADPRP) in nuclear DNA repair and other nuclear processes has been intensely studied and debated fo r decades, Recent studies have begun to shed new light on these argume nts with firm experimental data for its role, primarily, as a remodele r of chromatin structure. Those studies imply that PADPRP plays an ind irect role in DNA repair, serving to expose DNA to repair enzymes thro ugh chromatin remodeling. Only DNA that is tightly packaged would requ ire PADPRP activity for its repair while DNA in an open conformation w ould be accessible to DNA repair enzymes and not require PADPRP activi ty. The purpose of the current studies was to address the above hypoth esis directly, Using quantitative Southern blot analysis, we studied r epair in transcribed and nontranscribed nuclear DNA sequences in ADPRT 351 cells 95% deficient in PADPRP activity. Cells were exposed to met hylnitrosourea (MNU) for 1 h and allowed to repair for 8 or 24 h, Dens itometric scans of autoradiographs revealed that, when compared to the ir parental V79 cell line, ADPRT 351 cells 95% deficient in PADPRP act ivity were equally as efficient in repair of N-methylpurines in the tr anscribed sequence containing the dihydrofolate reductase gene. Howeve r, the ADPRT 351 cells were deficient in the ability to repair these l esions in the nontranscribed sequence containing the IgE gene compared to repair of the same sequence in the parental V79 cells. Nucleoid se dimentation assays demonstrated that the ADPRT 351 cells are deficient in repair across the entire genome when compared to the parental V79 cells. These studies indicate that PADPRP activity is not required for repair of N-methylpurines in transcribed nuclear DNA sequences but is necessary for the repair of these lesions in nontranscribed nuclear D NA sequences as well as across the entire genome since the DNA in a gi ven cell is predominantly nontranscribed.