Chromatin states at ribosomal DNA loci

Eukaryotic transcription of ribosomal RNAs (rRNAs) by RNA polymerase I can account for more than half of the total cellular transcripts depending on organism and growth condition. To support this level of expression, eukaryotic rRNA genes are present in multiple copies. Interestingly, these genes co-exist in different chromatin states that may differ significantly in their nucleosome content and generally correlate well with transcriptional activity. Here we review how these chromatin states have been discovered and characterized focusing particularly on their structural protein components. The establishment and maintenance of rRNA gene chromatin states and their impact on rRNA synthesis are discussed. This article is part of a Special Issue entitled: Transcription by Odd Pols.

► The ribosomal RNA (rRNA) genes transcribed by RNA polymerase I coexist in different chromatin states.
► Many structural and molecular features of the chromatin states are conserved in eukaryotes.
► The rRNA gene chromatin states are dynamic and respond to essential cellular processes.
► The maintenance of rRNA gene chromatin states is important to guarantee ribosome production and genome stability.