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Abstract
<p class="first" id="d14540536e63">A role for SUMOylation in the biogenesis and/or
function of Box C/D snoRNPs has been
reported, mediated via SUMO2 conjugation to the core snoRNP protein, Nop58. A quantitative
proteomics screen, based on SILAC (stable-isotope labeling by amino acids in cell
culture) and mass spectrometry using extracts prepared from cultured mammalian cells
expressing either 6His-SUMO1 or -SUMO2, revealed that the snoRNP-related proteins
Nop58, Nhp2, DKC1 and NOLC1 are amongst the main SUMO-modified proteins in the nucleolus.
SUMOylation of Nhp2 and endogenous Nop58 was confirmed using a combination of in vitro
and cell-based assays and the modified lysines identified by site-directed mutagenesis.
SUMOylation of Nop58 was found to be important for high-affinity Box C/D snoRNA binding
and the localization of newly transcribed snoRNAs to the nucleolus. Here, these findings
are reviewed and a model for understanding Nop58 SUMOylation in the context of Box
C/D snoRNP biogenesis is presented. Given the essential role of snoRNPs in the modification
of pre-ribosomal RNA, this work suggests that SUMO, snoRNPs and ribosome assembly,
and thus cellular translation, growth and proliferation, may be linked via novel mechanisms
which warrant further investigation.
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