Nap57, a mammalian nucleolar protein with a putative homolog in yeast and bacteria

U. Thomas Meier, Günter Blobel

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Abstract

We report the identification and molecular characterization of a novel nucleolar protein of rat liver. As shown by coimmunoprecipitation this protein is associated with a previously identified nucleolar protein, Nopp140, in an apparently stoichiometric complex and has therefore been termed NAP57 (Nopp140-associated protein of 57 kD). Immunofluorescence and immunogold electron microscopy with NAP57 specific antibodies show colocalization with Nopp140 to the dense fibrillar component of the nucleolus, to coiled bodies, and to the nucleoplasm. Imnmnogold staining in the nucleoplasm is occasionally seen in the form of curvilinear tracks between the nucleolus and the nuclear envelope, similar to those previously reported for Nopp140. These data suggest that Nopp140 and NAP57 are indeed associated with each other in these nuclear structures. The cDNA deduced primary structure of NAP57 shows a protein of a calculated molecular mass of 52,070 that contains a putative nuclear localization signal near its amino and carboxy terminus and a hydrophobic amino acid repeat motif extending across 84 residues. Like Nopp140, NAP57 lacks any of the known consensus sequences for RNA binding which are characteristic for many nucleolar proteins. Data bank searches revealed that NAP57 is a highly conserved protein. A putative yeast (S. cerevisiae) homolog is 71% identical. Most strikingly, there also appears to be a smaller prokaryotic (E. coli and B. subtilis) homolog that is nearly 50% identical to NAP57. This indicates that NAP57 and its putative homologs might serve a highly conserved function in both pro- and eukaryotes such as chaperoning of ribosomal proteins and/or of preribosome assembly.

Original languageEnglish (US)
Pages (from-to)1505-1514
Number of pages10
JournalJournal of Cell Biology
Volume127
Issue number6 I
DOIs
StatePublished - Dec 1994

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Nuclear Proteins
Yeasts
Bacteria
Proteins
Coiled Bodies
Nuclear Localization Signals
Amino Acid Motifs
Ribosomal Proteins
Nuclear Envelope
Consensus Sequence
Eukaryota
Fluorescent Antibody Technique
Saccharomyces cerevisiae
Electron Microscopy
Complementary DNA
Databases
RNA
Staining and Labeling
Escherichia coli
Antibodies

ASJC Scopus subject areas

  • Cell Biology

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Nap57, a mammalian nucleolar protein with a putative homolog in yeast and bacteria. / Meier, U. Thomas; Blobel, Günter.

In: Journal of Cell Biology, Vol. 127, No. 6 I, 12.1994, p. 1505-1514.

Research output: Contribution to journalArticle

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abstract = "We report the identification and molecular characterization of a novel nucleolar protein of rat liver. As shown by coimmunoprecipitation this protein is associated with a previously identified nucleolar protein, Nopp140, in an apparently stoichiometric complex and has therefore been termed NAP57 (Nopp140-associated protein of 57 kD). Immunofluorescence and immunogold electron microscopy with NAP57 specific antibodies show colocalization with Nopp140 to the dense fibrillar component of the nucleolus, to coiled bodies, and to the nucleoplasm. Imnmnogold staining in the nucleoplasm is occasionally seen in the form of curvilinear tracks between the nucleolus and the nuclear envelope, similar to those previously reported for Nopp140. These data suggest that Nopp140 and NAP57 are indeed associated with each other in these nuclear structures. The cDNA deduced primary structure of NAP57 shows a protein of a calculated molecular mass of 52,070 that contains a putative nuclear localization signal near its amino and carboxy terminus and a hydrophobic amino acid repeat motif extending across 84 residues. Like Nopp140, NAP57 lacks any of the known consensus sequences for RNA binding which are characteristic for many nucleolar proteins. Data bank searches revealed that NAP57 is a highly conserved protein. A putative yeast (S. cerevisiae) homolog is 71{\%} identical. Most strikingly, there also appears to be a smaller prokaryotic (E. coli and B. subtilis) homolog that is nearly 50{\%} identical to NAP57. This indicates that NAP57 and its putative homologs might serve a highly conserved function in both pro- and eukaryotes such as chaperoning of ribosomal proteins and/or of preribosome assembly.",
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