Organelles and compartments are distinguished by their biological functions, which in turn are reflected by their proteome profiles. Prerequisites for the organization of cellular compartments are mechanisms that help to generate and maintain their proper composition. The nucleolus is one of the compartments that have been the focus of intense research during the past years. It is now well-established that nucleoli are crucial for a growing number of diverse cellular processes. Moreover, it became clear that the functional organization of nucleoli is important for the survival and growth of cells under normal, stress and disease conditions. Recent research provided us with information on the nucleolar proteome under different physiological conditions. These studies demonstrated that multiple chaperone families, cochaperones and other folding factors are present in nucleoli. The exact functions chaperones have in the nucleolus are currently not understood; however, data provided by nucleolar proteomics put us in the position to study novel aspects of chaperone biology. These include the specific roles of chaperones in the nucleolus and the mechanisms that regulate their transport in and out of nucleoli. Our review summarizes the present knowledge of chaperones and their co-factors in the nucleolus as it is emerging from proteomics and other studies. Based on this information, we speculate on the biological relevance of chaperones in the nucleolus and the cellular pathways that promote their targeting to this subnuclear compartment. We conclude by highlighting the open questions that will have to be addressed in future studies.
Keywords: Proteomics, nucleolus, chaperones, protein transport, rheumatoid arthritis, polypeptides, Protein Folding, Apoptosis, Arabidopsis, Dictyostelium
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