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The nucleolus is a non-membrane bound nuclear compartement found in eukaryotic cells which is the site of ribosome biogenesis. The interphase nucleolus is organized around the tandemly repeated genes for preribosomal RNA (rRNA). It is composed of at least 2 sub-compartments: the dense fibrillar component (DFC, also called pars fibrosa) and the granular component (GC or pars granulosa). The DFC contains newly synthesized preribosomal RNA and a collection of proteins; the GC is made up of nearly completed preribosomal particles destined for the cytoplasm. In most metazoans, but generally not in lower eukaryotes, a third component, the fibrillar center (FC), can be seen. Plant and animal nuclei can contain more than one nucleolus.




› Cellular component


nucleolus [ GO:0005730 ]