In a paper published online in advance in Molecular Cell this week, researchers at the University of Zurich show that poly(ADP-ribose)-polymerase-1, or PARP1/ARTD1, "is implicated in the maintenance of silent rDNA chromatin during cell division." More specifically, the team shows that "PARP1 associates with TIP5 … via the noncoding pRNA and binds to silent rRNA genes after their replication in mid-late S phase," such that it represses rRNA transcription and plays a role in the formation of silent rDNA chromatin.