The interaction of DNA with proteins in the context of chromatin has to be 
tightly regulated to achieve so different tasks as packaging, transcription, 
replication and repair. The very rapid and transient post-translational 
modification of proteins by poly(ADP-ribose) has been shown to take part in all 
four. Originally identified as immediate cellular answer to a variety of 
genotoxic stresses, already early data indicated the ability of this highly 
charged nucleic acid-like polymer to modulate nucleosome structure, the basic 
unit of chromatin. At the same time the enzyme responsible for synthesizing 
poly(ADP-ribose), the zinc-finger protein poly(ADP-ribose) polymerase-1 (PARP1), 
was shown to control transcription initiation as basic factor TFIIC within the 
RNA-polymerase II machinery. Later research focused more on PARP-mediated 
regulation of DNA repair and cell death, but in the last few years, 
transcription as well as chromatin modulation has re-appeared on the scene. This 
review will discuss the impact of PARP1 on transcription and transcription 
factors, its implication in chromatin remodeling for DNA repair and probably 
also replication, and its role in controlling epigenetic events such as DNA 
methylation and the functionality of the insulator protein CCCTC-binding factor.