An abundant nucleolar phosphoprotein is associated with ribosomal DNA in Tetrahymena macronuclei.
An abundant 52-kDa phosphoprotein was identified and characterized from macronuclei of the ciliated protozoan Tetrahymena thermophila. Immunoblot analyses combined with light and electron microscopic immunocytochemistry demonstrate that this polypeptide, termed Nopp52, is enriched in the nucleoli of transcriptionally active macronuclei and missing altogether from transcriptionally inert micronuclei. The cDNA sequence encoding Nopp52 predicts a polypeptide whose amino-terminal half consists of multiple acidic/serine-rich regions alternating with basic/proline-rich regions. Multiple serines located in these acidic stretches lie within casein kinase II consensus motifs, and Nopp52 is an excellent substrate for casein kinase II in vitro. The carboxyl-terminal half of Nopp52 contains two RNA recognition motifs and an extreme carboxyl-terminal domain rich in glycine, arginine, and phenylalanine, motifs common in many RNA processing proteins. A similar combination and order of motifs is found in vertebrate nucleolin and yeast NSR1, suggesting that Nopp52 is a member of a family of related nucleolar proteins. NSR1 and nucleolin have been implicated in transcriptional regulation of rDNA and rRNA processing. Consistent with a role in ribosomal gene metabolism, rDNA and Nopp52 colocalize in situ, as well as by cross-linking and immunoprecipitation experiments, demonstrating an association between Nopp52 and rDNA in vivo.
McGrath
K E
KE
Department of Biology, University of Rochester, New York 14627, USA.
Smothers
J F
JF
Dadd
C A
CA
Madireddi
M T
MT
Gorovsky
M A
MA
Allis
C D
CD
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D047390:Casein Kinase II; D002466:Cell Nucleolus / Q000737:chemistry* / Q000378:metabolism; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism*; D003432:Cross-Linking Reagents; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000378:metabolism*; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015800:Protozoan Proteins; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D016808:Tetrahymena thermophila / Q000737:chemistry*; D014158:Transcription, Genetic; D014714:Vertebrates; D000097796:Nucleolin
D047390:Casein Kinase II; D003432:Cross-Linking Reagents; D018076:DNA, Complementary; D004275:DNA, Ribosomal; D005656:Fungal Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D015800:Protozoan Proteins; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D000097796:Nucleolin; C105068:NOPP52 protein, Tetrahymena thermophila; C068036:NSR1 protein, S cerevisiae