Nucleolin, the major nucleolar protein of growing eukaryotic cells: an unusual protein structure revealed by the nucleotide sequence.

Abstract

Nucleolin (also called C23) is the major nucleolar protein of exponentially growing eukaryotic cells. It is found associated with intranucleolar chromatin and preribosomal particles. Through use of a polyclonal antiserum, nucleolin cDNA clones were isolated from a Chinese hamster ovary cell library constructed in the expression vector Xgtll. The isolated cDNAs encoded a polypeptide containing 679 residues of the 713 amino acids of nucleolin. The amino acid sequence presents several unusual features: in particular, repetitive sequences are found at both ends of the molecule. A repeat, Hy-Thr-Pro-Hy-Lys-Lys-Hy-Hy, in which Hy is a nonpolar residue, is found six times in the NH2-end proximal portion, followed by three acidic stretches containing 25, 25, and 33 glutamic acid or aspartic acid residues. Four potential phosphorylation sites (serines) are also observed in this region. The COOH-terminal proximal portion of the protein carries a glycine-rich region with fairly regularly interspersed phenylalanine and dimethylarginine residues. The two terminal portions of the molecule exhibit unique potential secondary structures: a-helix (NH2 terminus) and extended (COOH terminus). The central region exhibits alternating hydrophobic and hydrophilic stretches. Five potential N glycosylation sites are detected. The structure of this protein may reflect two functions in preribosome biogenesis: interaction with chromatin (NH2 terminus) and with preribosomes (COOH terminus).

NAP‐I is a functional homologue of TAF‐I that is required for replication and transcription of the adenovirus genome in a chromatin‐like structure

“…For example, the SWI/SNF complex facilitates the binding of the TATAbinding protein (TBP) to the TATA box . Chromatin structure is also regulated by a variety of proteins including histone chaperones and the proteins involved in nucleosome assembly (Krohne & Franke 1980;Lapeyre et al 1987;Shirakawa & Yoshida 1992). Nucleoplasmin and N1, which associate with H2A and H2B and with H3 and H4, respectively, were isolated from the eggs of Xenopus laevis.…”

Cell Cycle-controlled Interaction of Nucleolin with the Retinoblastoma Protein and Cancerous Cell Transformation

“…A role of nucleolin in activation as well as repression of ribosomal RNA synthesis has been described (1,66). Thus far, it has not been completely elucidated how the intracellular distribution of nucleolin is controlled.…”

“…Nucleolin is a multifunctional protein that is found in the nucleolus, in the nucleus, in the cytoplasm, and at the cell surface (1,3,5,64,65). A role of nucleolin in activation as well as repression of ribosomal RNA synthesis has been described (1,66).…”

An abundant nucleolar phosphoprotein is associated with ribosomal DNA in Tetrahymena macronuclei.

“…In this study, we report the identification and characterization of a prominent macronuclearspecific phosphoprotein enriched in Tetrahymena nucleoli. The cDNA sequence encoding this 52-kDa polypeptide (termed Nopp52) predicts a domain structure similar to other nucleolar proteins, especially vertebrate nucleolin and yeast NSR1 (Lapeyre et al, 1987;Lee et al, 1991). In situ hybridization to rDNA and immunocytochemical localization of Nopp52 indicates these components are colocalized in nucleoli.…”