Chromatin organization of active ribosomal RNA genes

Eukaryotic cells contain several hundred copies of the ribosomal RNA genes co-existing in two distinct chromatin conformations-an active conformation permissive to transcription and an inactive conformation refractive to transcription. Whereas silencing of rRNA gene transcription has been partly uncovered, the epigenetic mechanisms leading to the active rRNA gene chromatin structure are less well understood. Here we discuss recent studies addressing the local and higher order structure of active rRNA gene chromatin.