title: Dual function for poly(ADP-ribose) synthesis in response to DNA strand breakage.
abstract: Soluble extracts of human cells repair gamma-ray-induced single-strand breaks in DNA. Accompanying NAD-dependent automodification of poly(ADP-ribose) polymerase is required for effective DNA rejoining. The kinetics of poly(ADP-ribose) synthesis by this polymerase, and subsequent polymer degradation by poly(ADP-ribose) glycohydrolase, have been compared with the rate of DNA repair. The results agree with previous in vivo data. In response to addition of gamma-irradiated plasmid DNA, rapid and heavy automodification of poly(ADP-ribose) polymerase occurred in NAD-containing human cell extracts. After 2 min at 30 degrees C, when very little DNA rejoining had yet occurred, synthesis of long polymers essentially ceased, although only a minor fraction of the NAD had been consumed. Poly(ADP-ribose) chains were then reduced to oligomer size by poly(ADP-ribose) glycohydrolase. These short chains were present for longer times and were sufficient to permit DNA repair. Thus, most but not all poly(ADP-ribose) synthesis could be suppressed without marked inhibition of DNA repair, and prolonged occurrence of long poly(ADP-ribose) chains in consequence to glycohydrolase inhibition did not improve DNA repair. The temporary presence of short poly(ADP-ribose) chains on poly(ADP-ribose) polymerase avoids inhibition of excision-repair by that protein, but the initial very transient formation of long and branched chains of poly(ADP-ribose) in response to DNA damage apparently serves an entirely different purpose. Local poly(ADP-ribose) synthesis in the vicinity of a DNA strand interruption causes negative charge repulsion, and this may function to prevent accidental homologous recombination events within tandem repeat DNA sequences.
authors.affiliation: Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms, Hertfordshire, U.K.
authors.forename: M S
authors.initials: MS
authors.lastname: Satoh
authors.forename: G G
authors.initials: GG
authors.lastname: Poirier
authors.forename: T
authors.initials: T
authors.lastname: Lindahl
mesh_terms: D002460:Cell Line; D004249:DNA Damage; D004260:DNA Repair; D004274:DNA, Recombinant / Q000528:radiation effects; D006801:Humans; D011064:Poly Adenosine Diphosphate Ribose / Q000096:biosynthesis*
chemical_list: D004274:DNA, Recombinant; D011064:Poly Adenosine Diphosphate Ribose