FIGURE 2.

The epigenetic control of rRNA: pRNA and PAPAS RNAPI binding to rDNA promoter gives rise to the transcription of pRNA, whose sequences match that of rDNA promoter. In contrast, the antisense transcription of rDNA, mediated by RNAPII, gives rise to PAPAS, spanning from rDNA gene body to intergenic, promoter, and enhancer regions (Figure, central panel). pRNA can mediate the silencing of rDNA loci by (A) directly recruiting DNMT3b, leading to de novo methylation and heterochromatinization; (B) binding NoRC and HDAC, promoting nucleosome sliding and deacetylation, respectively. (C) PAPAS leads to rDNA silencing by recruiting SUV4 on rDNA promoter. (D) PAPAS can associate with the chromatin remodeling complex CHD4/NuRD and guide it on the rDNA locus to promote nucleosome shifting and transcriptional repression of rDNA in a heat stress-dependent manner.