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Beschreibung

Nucleolin (UniProt: P19338, also known as Protein C23) is encoded by the NCL gene (Gene ID: 4691) in human. Nucleolin is a highly conserved, multi-functional, phosphoprotein that is ubiquitously distributed in the nucleolus, nucleus and cytoplasm. It is associated with intranucleolar chromatin and pre-ribosomal particles. In the cytoplasm, it is localized in cytoplasmic mRNP granules containing untranslated mRNA. Its levels are correlated with the rate of functional activity of the nucleolus in exponentially growing cells. Nucleolin contains three structural and multifunctional domains: An N-terminal portion containing several acidic stretches, two to four RNA-binding domains known as RNA recognition motifs (RRM) in the central region, and a glycine/arginine-rich domain at the C-terminus. The N-terminal acidic and basic region and the C-terminal domain rich in glycine/arginine repeats are reported to mediate protein-protein interactions with histone H1, U3 snoRNP and ribosomal proteins. Nucleolin contains intrinsic DNA and RNA helicase, nucleic-acid-dependent ATPase, and self-cleaving activities. It is known to bind RNA through its RRMs. It binds RNA oligonucleotides with 5'-UUAGGG-3' repeats more tightly than the telomeric single-stranded DNA 5'-TTAGGG-3' repeats. Nucleolin participates in regulation of various aspects of DNA and RNA metabolism, chromatin structure, rDNA transcription, rRNA maturation, cytokinesis, nucleogenesis, cell proliferation and growth. It is also involved in the folding, maturation and ribosome assembly, and nucleocytoplasmic transport of newly synthesized pre-RNAs, gene silencing and senescence. The phosphorylation state of nucleolin is highly regulated during the cell cycle. Extensive phosphorylation by casein kinase 2 is shown to occur at interphase and by CDC2 during mitosis. (Ref.: Abdelmohsen, K., and Gorospe, M. (2012). RNA Biol. 9(6), 799-808, Tajrishi, MM., et al. (2011). Commun. Integr. Biol. 4(3), 267-275).