N-terminal domains of plant poly(ADP-ribose) polymerases define their association with mitotic chromosomes

Poly(ADP-ribos)ylation is a reversible protein modification that in higher plants is catalyzed by two structurally different poly(ADP-ribose) polymera ses, App and Zap. In vivo imaging of green-fluorescent protein (GPF) fusion s showed that both Zap and App were associated with chromatin through the c ell cycle progression. The in vivo behaviour of the App-GFP protein fusions can be attributed to the activity of two NASA motifs that mediate protein- protein interactions and nucleic acid binding. Expression of Zap deletion v ariants revealed that both Zn fingers and helix-turn-helix domains contribu ted to the association with chromosomes, whereas the localization in the nu cleoplasm was mostly determined by the Zn fingers. The results highlight no vel properties of protein sequences found in plant poly(ADP-ribose) polymer ases and suggest important functions for this class of nuclear enzymes in c hromosome dynamics.