FIGURE 4.

Specific residues of the Zn1 base stacking loop are required for DNA-dependent PARP-1 activation. A, detailed view of the Zn1 base stacking loop. B, DNA-dependent automodification assay using a combination of WT or mutant Zn1 domain, the ΔZn1 fragment of PARP-1, 5 mm NAD⁺, and the absence or presence of 1 μm DNA. Time points were analyzed on 15% SDS-PAGE with Coomassie staining. C, DNA-dependent automodification activity of full-length PARP-1 bearing mutations in the Zn1 domain. Time points were analyzed on 12% SDS-PAGE with Coomassie staining.