Faithful propagation of specific chromatin states requires re-establishment of epigenetic marks after every cell division. How the original epigenetic signature is inherited after disruption during DNA replication is still poorly understood. Here, we show that the poly(ADP-ribose)-polymerase-1 (PARP1/ARTD1) is implicated in the maintenance of silent rDNA chromatin during cell division. We demonstrate that PARP1 associates with TIP5, a subunit of the NoRC complex, via the noncoding pRNA and binds to silent rRNA genes after their replication in mid-late S phase. PARP1 represses rRNA transcription and is implicated in the formation of silent rDNA chromatin. Silent rDNA chromatin is a specific substrate for ADP-ribosylation and the enzymatic activity of PARP1 is necessary to establish rDNA silencing. The data unravel a function of PARP1 and ADP-ribosylation that serves to allow for the inheritance of silent chromatin structures, shedding light on how epigenetic marks are transmitted during each cell cycle.
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