Schematic models for the role of PCAF and CSB in rRNA transcription.

<p>Deacetylation of H4 and H3K9 are associated with poised rDNA promoters, whereas acetylation of H4 and H3K9 are restricted to rDNA promoters in active state. After conversion of poised rDNA promoters to active ones, PCAF is recruited to active state of rRNA promoters by CSB, and induces acetylation of histones to promote association of RNA polymerase I with rDNA promoters, thereby facilitating the initiation of rDNA transcription.