Chromatin organization and the mammalian nucleolus

Abstract

The nucleolus is the largest compartment of the cell nucleus where ribosomal RNAs (rRNAs) are synthesized, processed and assembled with ribosomal proteins. In addition to rRNA gene clusters that build the core of this subnuclear structure, nucleoli are surrounded by a shell of condensed chromatin. Although the higher-order structures of rRNA genes and nucleolus-associated chromatin have been studied for decades, detailed molecular insights into the constituents and organization of the nucleolar genome are only beginning to emerge. Here, we summarize current views on the structural organization of nucleolar chromatin with a special emphasis on its protein components.