lncRNA-Induced Nucleosome Repositioning Reinforces Transcriptional Repression of rRNA Genes upon Hypotonic Stress.

The activity of rRNA genes (rDNA) is regulated by pathways that target the transcription machinery or alter the epigenetic state of rDNA. Previous work has established that downregulation of rRNA synthesis in quiescent cells is accompanied by upregulation of PAPAS, a long noncoding RNA (lncRNA) that recruits the histone methyltransferase Suv4-20h2 to rDNA, thus triggering trimethylation of H4K20 (H4K20me3) and chromatin compaction. Here, we show that upregulation of PAPAS in response to hypoosmotic stress does not increase H4K20me3 because of Nedd4-dependent ubiquitinylation and proteasomal degradation of Suv4-20h2.

Quiescence-induced LncRNAs trigger H4K20 trimethylation and transcriptional silencing.

A complex network of regulatory pathways links transcription to cell growth and proliferation. Here we show that cellular quiescence alters chromatin structure by promoting trimethylation of histone H4 at lysine 20 (H4K20me3). In contrast to pericentric or telomeric regions, recruitment of the H4K20 methyltransferase Suv4-20h2 to rRNA genes and IAP elements requires neither trimethylation of H3K9 nor interaction with HP1 proteins but depends on long noncoding RNAs (lncRNAs) that interact with Suv4-20h2.