Within the nucleus, the nucleolus is a dynamic compartment which is critical to maintain cellular homeostasis
under normal, stress and disease conditions. During the last years, proteomics research provided new information on the
complexity of nucleolar proteomes. These studies also established that many chaperones, co-chaperones and other factors
involved in proteostasis associate with nucleoli in the absence of stress or disease. Moreover, quantitative proteomics
demonstrated that physiological and environmental changes alter the nucleolar profile of chaperones and co-chaperones.
At present, the emphasis has shifted towards sophisticated in-depth analyses of the nucleolar proteome. As such, turnover
and posttranslational modifications are now quantified for individual proteins that associate with nucleoli. This large body
of work generated new insights into the sumoylation, phosphorylation and acetylation of the nucleolar proteome. At the
same time, we have gained a better understanding of the nucleolar organization, as novel subcompartments were identified
within the nucleolus that are induced by physiological and other forms of stress. Notably, some of these subcompartments
are also enriched for chaperones. To review these results, we will focus on recent studies that analyzed the nucleolar
proteome, and particular emphasis will be given to nucleolar chaperones. Despite remarkable progress in the field, crucial
questions regarding the physiological relevance of nucleolar chaperones remain to be answered in the years ahead.
We conclude our update by discussing these future directions in the context of the latest developments in the nucleolar
and chaperone fields.
Keywords: Chaperones, proteomics, nucleolus, T-complex protein, Small ubiquitin-like modifier, NAD-dependent deacetylase sirtuin-7, Stable isotope labeling with amino acids in cell culture, Peptidyl-prolyl isomerases, RNA polymerase I, transcribes rDNA, Prefoldin, Protein disulfide isomerases, Granular component, Heat shock protein, Bcl2-associated athanogene
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