Specific Binding of Poly(ADP-ribose) Polymerase-1 to Cruciform Hairpins

Poly(ADP-ribose) polymerase-1 (PARP-1) participates in DNA cleavage and rejoining-dependent reactions, such as DNA replication, recombination and repair. PARP-1 is also important in transcriptional regulation, although the determinants for its binding to undamaged genomic DNA have not been defined. Previously, we have shown by low-resolution mapping that PARP-1 may bind to the cruciform-forming regions of its own promoter. Here, using DNase I and nuclease P1 footprinting and atomic force microscopy, we show that PARP-1 binds to stem/loop boundaries of cruciform hairpins. Cleavage of the cruciform by the junction resolvase T4 endonuclease VII is independent of PARP-1, which indicates that PARP-1 does not bind to the four-arm junctions of the cruciform. Thus, PARP-1 differs from other cruciform-binding proteins by binding to hairpin tips rather than to junctions. Furthermore, our data indicate that PARP-1 can interact with the gene regulatory sequences by binding to the promoter-localized cruciforms.