The N-terminal fragment of PARP-1, produced by GzmA cleavage, interferes with DNA repair. (A) The N-terminal, but not C-terminal, fragment of GzmA-cleaved PARP-1 binds to DNA by gel shift. The protein-DNA complex is supershifted by PARP-1 (P) antiserum, but not control (C) antiserum. (B) The N-terminal fragment persists in cells treated with GzmA and PFN. Cell lysates were analyzed by immunoblot probed with an antibody that recognizes the N terminus of PARP-1. (C) Overexpressing PARP^1-498 in HeLa cells enhances DNA damage induced by either GzmA and PFN (left) or MNNG (right) by comet assay, whereas overexpressing WT PARP enhances DNA repair. PARP^499-1014, which lacks the DNA binding domains, has no effect. N.S. = not significant. Representative data from at least 3 independent experiments are shown.