Distinct domains of a nucleolar protein mediate protein kinase binding, interaction with nucleic acids and nucleolar localization.
Nopp44/46 is a phosphoprotein of the protozoan parasite Trypanosoma brucei that is localized to the nucleolus. Based on the primary sequence, Nopp44/46 appears to be a protein composed of distinct domains. This communication describes the relationship of these domains to the known functional interactions of the molecule and suggests that the amino-terminal region defines a novel homology region that functions in nucleolar targeting. We have previously shown that Nopp44/46 is capable of interacting with nucleic acids and associating with a protein kinase. Using in vitro transcription and translation, we now demonstrate that the nucleic acid binding function maps to the carboxy-terminal domain of the molecule, a region rich in arginine-glycine-glycine motifs. Our experiments reveal that a central region containing a high proportion of acidic residues is required for association with the protein kinase. Analysis of transfectants expressing epitope-tagged Nopp44/46 deletion constructs showed that the amino-terminal 96 amino acids allowed nuclear and nucleolar accumulation of the protein. This region of the molecule shows homology to several recently described nucleolar proteins. Deletion of a 27-amino-acid region within this domain abrogated nucleolar, but not nuclear, localization. These studies show that Nopp44/46 is composed of distinct modules, each of which plays a different role in molecular interactions. We suggest that this protein could facilitate interactions between sets of nucleolar molecules.
Seattle Biomedical Research Institute, Seattle, WA 98109, USA.
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A
Das
J H
JH
Park
C B
CB
Hagen
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Parsons
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000235:genetics; D002466:Cell Nucleolus / Q000201:enzymology* / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009696:Nucleic Acids / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding / Q000235:genetics; D011494:Protein Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014346:Trypanosoma brucei brucei
C100391:NOPP44-46 protein, Trypanosoma brucei; D009687:Nuclear Proteins; D009696:Nucleic Acids; D010750:Phosphoproteins; D015800:Protozoan Proteins; D016601:RNA-Binding Proteins; D011494:Protein Kinases