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Nucleolus

  1. Peter J Shaw

Published Online: 15 NOV 2010

DOI: 10.1002/9780470015902.a0001352.pub3

eLS

eLS

How to Cite

Shaw, P. J. 2010. Nucleolus. eLS. .

Author Information

  1. John Innes Centre, Norwich, Norfolk, UK

Publication History

  1. Published Online: 15 NOV 2010

This is not the most recent version of the article. View current version (16 NOV 2015)

Abstract

The nucleolus is a nuclear substructure where the genes for three of the four ribosomal ribonucleic acids (RNAs) are transcribed and where ribosomal subunits are assembled. Although the nucleolus has been intensively studied for many years, recent progress has been very rapid. We are beginning to understand how the biochemical processes carried out in the nucleolus relate to the observable structure. There is much emerging evidence that the nucleolus is also involved in many other roles, particularly in the biogenesis of RNA-containing complexes, in stress sensing and in the control of cellular activity and proliferation. Recent observations of nucleolar proteins in living cells have shown that the nucleolus and its components are highly dynamic and that the observed structure is a steady state result of the dynamic diffusion of proteins and other macromolecules throughout the nucleoplasm and nucleolus and their relative residence times in the various locations.

Key Concepts:

  • The nucleolus is the clearest subnuclear structure in most eukaryotic cells and is the site of rDNA transcription and ribosome biosynthesis.

  • Most nucleoli show three types of substructural components in standard thin section transmission electron microscopy: fibrillar centres (FC), dense fibrillar component (DFC) and granular component (GC).

  • The interpretation of nucleolar ultrastructure in functional terms is still not fully understood, but rDNA transcription occurs within the DFC, and the subsequent stages of rRNA processing occur vectorially in enveloping layers as the transcripts move away from the transcription sites.

  • Nucleoli share factors and, possibly, processes with other subnuclear structures, particularly Cajal bodies.

  • Most nucleolar proteins are highly dynamic and diffuse freely through the nucleolus and nucleoplasm; ‘nucleolar’ proteins have a residence time in the nucleolus of the order of a few tens of seconds.

  • The nucleolus is involved in many other nonconventional activities such as biogenesis of other RNP complexes, mRNA surveillance, stress sensing and control of cell proliferation.

Keywords:

  • ribosomal RNA;
  • RNA polymerase I;
  • nucleolar organisation;
  • ribosome biosynthesis