sentences:  PARP1, a poly-ADP ribose polymerase, has been shown to affect chromatin structure and promote changes in the organization of nucleosomes through modification of histones.PARPs have been shown to affect transcription factor structure and cause recruitment of many transcription factors to form complexes at DNA and elicit transcription.Mono ADP-ribosyltransferases are also shown to affect transcription factor binding at promoters.