Establishment and Maintenance of Open Ribosomal RNA Gene Chromatin States in Eukaryotes
Christopher Schächner, Philipp Merkl, Michael Pilsl, Katrin Schwank, Kristin Hergert, Sebastian Kruse, Philipp Milkereit, Herbert Tschochner, Joachim Griesenbeck
Abstract
In growing eukaryotic cells, nuclear ribosomal (r)RNA synthesis by RNA polymerase (RNAP) I accounts for the vast majority of cellular transcription. This high output is achieved by the presence of multiple copies of rRNA genes in eukaryotic genomes transcribed at a high rate. In contrast to most of the other transcribed genomic loci, actively transcribed rRNA genes are largely devoid of nucleosomes adapting a characteristic "open" chromatin state, whereas a significant fraction of rRNA genes resides in a transcriptionally inactive nucleosomal "closed" chromatin state. Here, we review our current knowledge about the nature of open rRNA gene chromatin and discuss how this state may be established.